Three-dimensional imaging using a fluorescent medium

ABSTRACT

The attenuation and other optical properties of a medium are exploited to measure a thickness of the medium between a sensor and a target surface. Disclosed herein are various mediums, arrangements of hardware, and processing techniques that can be used to capture these thickness measurements and obtain three-dimensional images of the target surface in a variety of imaging contexts. This includes general techniques for imaging interior/concave surfaces as well as exterior/convex surfaces, as well as specific adaptations of these techniques to imaging ear canals, human dentition, and so forth.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit U.S. Provisional Patent ApplicationsNo. 61/083,394 filed on Jul. 24, 2008 and U.S. Provisional PatentApplication No. 61/165,708 filed on Apr. 1, 2009, each of which ishereby incorporated by reference in its entirety.

BACKGROUND

Various techniques have been disclosed for capturing thicknessmeasurements using Emission Reabsorption Laser Induced Fluorescence(“ERLIF”) as described for example in the following literature, allincorporated by reference herein in its entirety: Hidrovo, C, Hart, D.P., “Excitation Non-Linearities in Emission Reabsorption Laser InducedFluorescence (ERLIF) Techniques,” Journal of Applied Optics, Vol. 43,No. 4, February 2004, pp. 894-913; Hidrovo, C., Hart, D. P., “2-DThickness and Temperature Mapping of Fluids by Means of a Two Dye LaserInduced Fluorescence Ratiometric Scheme,” Journal of Flow Visualizationand Image Processing, Volume 9, Issue 2, June 2002; Hidrovo, C., Hart,D. P., “Emission Reabsorption Laser Induced Fluorescence for FilmThickness Measurement,” Measurement Science and Technology, Vol. 12, No.4, 2001, pp. 467-477; and Hidrovo, C., Hart, D. P., “Dual Emission LaserInduced Fluorescence Technique (DELIF) for Oil Film Thickness andTemperature Measurement,” ASME/JSME Fluids Engineering Division SummerMeeting, Jul. 23-28, 2000, Boston, Mass.

While these existing techniques provide a useful approach for obtainingthickness measurements, they rely on various mixtures of two or morefluorescent dyes. There remains a need for other thickness measurementtechniques that do not require the use of multiple dyes, as well astechniques for adapting thickness measurements to various physicalcontexts for three-dimensional imaging.

SUMMARY

The attenuation and other optical properties of a medium are exploitedto measure a thickness of the medium between a sensor and a targetsurface. Disclosed herein are various mediums, arrangements of hardware,and processing techniques that can be used to capture these thicknessmeasurements and obtain three-dimensional images of the target surfacein a variety of imaging contexts. This includes general techniques forimaging interior/concave surfaces as well as exterior/convex surfaces,as well as specific adaptations of these techniques to imaging earcanals, human dentition, and so forth.

In one aspect, a method for obtaining three-dimensional data that isdisclosed herein includes distributing a medium between a target surfaceand a sensor, the medium including a single fluorescent substance havinga fluorescence emission spectrum that overlaps in wavelength with anon-zero absorption spectrum of the medium; exciting the singlefluorescent substance to provide a fluorescent emission; measuring thefluorescent emission with the sensor in a direction of a location on thetarget surface, including measuring an intensity at a first wavelengthand an intensity at a second wavelength, wherein the medium has adifferent coefficient of attenuation for the first wavelength and thesecond wavelength; and determining a thickness of the medium in thedirection of the location based upon a function of the intensity of thefirst wavelength and the intensity of the second wavelength. The mediummay have zero absorption at the second wavelength. The singlefluorescent substance may be fluorescein sodium. The first wavelengthmay be about 510 nanometers and the second wavelength is about 540nanometers. The single fluorescent substance may include quantum dots.The medium may include at least one of a liquid, a gas, a solid, and agel. When the medium is a gas, the method may further comprise providinga transparent barrier between the target surface and the sensor toretain the gas against the target surface. When the medium is a liquid,the method may further comprise immersing the target surface in theliquid; and positioning the sensor above a top surface of the liquid.Determining the thickness may include calculating a ratio of theintensity of the first wavelength to the intensity of the secondwavelength. The sensor may measure the intensity of the first wavelengthand the intensity of the second wavelength from a plurality of locationson the target surface at a corresponding plurality of pixel locationswithin the sensor, thereby providing a two-dimensional array ofthickness measurements. The method for obtaining three-dimensional datamay include constructing a three-dimensional image of a region ofinterest with a plurality of measurements from the sensor. The methodmay include constructing a three-dimensional image of the target surfacefrom a plurality of three-dimensional images of a plurality of regionsof interest. Exciting the single fluorescent substance may includedirecting a broadband light source toward the single fluorescentsubstance. Exciting the single fluorescent substance may includedirecting a light emitting diode toward the single fluorescentsubstance.

In one aspect, a device that is disclosed herein includes a targetsurface having a region of interest; a sensor positioned to measure anintensity at a first wavelength and an intensity at a second wavelengthin a direction of a location in the region of interest; a mediumdistributed between the target surface and the sensor, the mediumincluding a single fluorescent substance having a fluorescence emissionspectrum that overlaps in wavelength with a non-zero absorptionspectrum, wherein the medium has a different coefficient of attenuationfor the first wavelength and the second wavelength; a light sourcepositioned to excite the single fluorescent substance to provide afluorescent emission; and a processor programmed to calculate athickness of the medium in the direction of the location based upon afunction of the intensity of the first wavelength and the intensity ofthe second wavelength. The single fluorescent substance may befluorescein sodium. The single fluorescent substance may include quantumdots.

In one aspect, a system that is disclosed herein includes a distributingmeans for distributing a medium between a target surface and a sensor,the medium including a single fluorescent substance having afluorescence emission spectrum that overlaps in wavelength with anon-zero absorption spectrum; an illuminating means for exciting thesingle fluorescent substance to provide a fluorescent emission; a sensormeans for measuring the fluorescent emission with the sensor in adirection of a location on the target surface, including measuring anintensity at a first wavelength and an intensity at a second wavelength,wherein the medium has a different coefficient of attenuation for thefirst wavelength and the second wavelength; and a processing means forcalculating a thickness of the medium in the direction of the locationbased upon a function of the intensity of the first wavelength and theintensity of the second wavelength. The single fluorescent substance maybe fluorescein sodium. The single fluorescent substance may includequantum dots.

BRIEF DESCRIPTION OF THE FIGURES

The invention and the following detailed description of certainembodiments thereof may be understood by reference to the followingfigures:

FIG. 1 shows a three-dimensional imaging system.

FIG. 2 shows the emission and absorption spectra for fluorescein sodium.

FIG. 3 shows a three-dimensional imaging system using a luminescentsurface applied to an object.

FIG. 4 shows a three-dimensional imaging system using a passive surfaceapplied to an object.

FIG. 5 is a flow chart of a method for three-dimensional imaging using afluorescent layer applied to a target surface of an object.

FIG. 6 is a flow chart of a method for three-dimensional imaging using asingle fluorescent dye.

FIG. 7 is a flow chart of a method for three-dimensional imaging basedupon absorption.

FIG. 8 illustrates a computer-implemented method for three-dimensionalimaging using the technique described above.

FIG. 9 shows a method for using a single camera to measure thickness.

FIG. 10 illustrates an adaptation of the techniques described herein toimaging of an interior space such as a human ear canal.

FIG. 11 is a flow chart of a method for obtaining a three-dimensionalimage of an interior space.

FIG. 12 shows a self-inflating bladder for use in interior measurements.

FIG. 13 is a flow chart of a method for using a self-inflating bladderto capture three-dimensional images of an interior space.

FIG. 14 illustrates an adaptation of the techniques described herein tocapture a three-dimensional image of an object such as human dentition.

FIG. 15 is a flow chart of a method for capturing a three-dimensionalimage of an object such as human dentition using the techniquesdescribed herein.

DETAILED DESCRIPTION

Disclosed herein are various techniques for obtaining thicknessmeasurements from a film, liquid, gel, gas, or other medium based uponthe relationship between an intensity of light measured at two or moredifferent wavelengths. Also disclosed herein are various techniques forcapturing such thickness measurements in interior volumes (such as earcanals), exterior volumes (such as teeth), and so forth for use inthree-dimensional reconstruction. In general, the systems and methodsdescribed below exploit the Beer-Lambert Law for absorption of light ina medium, and more particularly, derivations based upon the Beer-LambertLaw where one wavelength is attenuated more than another as it passesthrough a medium. By controlling sources of light and the properties ofthe medium, this differential attenuation can be used to determine adistance that light travels through a medium to a sensor. More specificapplications of this general principle are provided below, and serve tooutline several variations of a new technique for distance measurementbased upon differential attenuation of various wavelengths of light.

Throughout this disclosure, the term “absorption” is used to describe anattenuation of energy such as electromagnetic energy propagating througha medium. This attenuation may be caused by physical absorption in themedium, or by any other physical phenomenon (such as scattering) orcombination of phenomena that result in a measurable decrease inintensity of a signal as it passes through the medium. For example, itwill be understood that in some embodiments—such as those involving goldnanoparticles as described herein—“absorption” is the result of multipleinelastic scattering events. Thus as used herein absorption should beunderstood broadly to refer to any form or cause of attenuation (or lackthereof) unless a more specific meaning is explicitly provided orotherwise clear from the context.

In the following description, terms such as thickness, thicknesscalculation, and thickness measurement are used interchangeably todescribe the thicknesses as determined using the techniques disclosedherein. In general, no particular meaning should be ascribed to theterms “measurement” and “calculation”, and the use of one term or theother, or similar references to “determining”, “calculating”, or“obtaining” thickness measurement, is not intended to imply anydistinction among the manners in which thickness might be determined.Rather, all such references to thickness should be understood to includeall of the techniques described herein for determining thickness of amedium or the length of an optical path therethrough, except where amore specific meaning is explicitly provided.

Throughout this disclosure, various terms of quantitative andqualitative description are used. These terms are not intended to assertstrict numerical boundaries on the features described, but rather shouldbe interpreted to permit some variability. Thus for example where mediumis described as being transparent at a particular wavelength, thisshould be understood to mean substantially transparent or sufficientlytransparent to permit measurements yielding accurate thicknesscalculations, rather than absolutely transparent at the limits ofmeasurement or human perception. Similarly, where a target surface isdescribed as having uniform color or a dye is described as fluorescingat a particular wavelength, this should not be interpreted to excludethe variability typical of any conventional material or manufacturingprocess. Thus in the following description, all descriptive terms andnumerical values should be interpreted as broadly as the nature of theinvention permits, and will be understood by one of ordinary skill inthe art to contemplate a range of variability consistent with properoperation of the inventive concepts disclosed herein, unless a differentmeaning is explicitly provided or otherwise clear from the context.

In the following description, the term wavelength is used to describe acharacteristic of light or other electromagnetic energy. It will beunderstood that the term wavelength may refer to a specific wavelength,such as where the description refers to a center frequency or a limit orboundary for a range of frequencies. The term may also or instead refergenerally to a band of wavelengths, such as where a wavelength isspecified for a sensor, pixel, or the like. Thus in general the termwavelength as used herein should be understood to refer to either orboth of a specific wavelength and a range of wavelengths unless a morespecific meaning is provided or otherwise clear from the context.

All documents mentioned herein are hereby incorporated by reference intheir entirety. References to items in the singular should be understoodto include items in the plural, and vice versa, unless explicitly statedotherwise or clear from the text. Grammatical conjunctions are intendedto express any and all disjunctive and conjunctive combinations ofconjoined clauses, sentences, words, and the like, unless otherwisestated or clear from the context.

Although the following disclosure includes example embodiments, theseexamples are provided for illustration only and are not intended in alimiting sense. All variations, modifications, extensions, applications,combinations of components, and the like as would be apparent to one ofordinary skill in the art are intended to fall within the scope of thisdisclosure.

FIG. 1 shows a three-dimensional imaging system. In an embodiment, thesystem 100 may employ a fluorescent medium between an object and acamera, although it will be readily appreciated that a variety ofmediums, sensors, and other components may be used. The system 100 mayinclude an excitation source 102 with a source filter 104, a medium 106,an object 108 with a target surface 110, a sensor 112 with a sensorfilter 114, and a computer 116. In general operation, the excitationsource 102 illuminates the object 108 along an optical illumination path118 through the medium 106, and the sensor 112 captures reflected lightfrom the object 108 on an optical return path 120 through the medium106. The resulting signal at the sensor 112 can be processed by thecomputer 116 to obtain thickness measurements of the medium 106, whichcan be further processed to obtain a three-dimensional image of theobject 108. It will be understood that numerous variations, additions,omissions, and modifications are possible, all as described in thevarious detailed embodiments set out below.

The excitation source 102 may be any suitable light source. In variousembodiments, this may include light emitting diodes, incandescent bulbsor lamps, laser light sources, or any other broadband light source,broadband visible light source, narrowband light source or anycombination of the foregoing that emits photons at the desiredwavelength(s). The excitation source 102 (as shaped by the source filter104) may provide light at any suitable wavelength(s) includingwavelengths that excite a fluorescent substance in the medium 106 or onthe target surface 110, as well as wavelength(s) having knownattenuation by the medium 106, all as more generally described below.The excitation source 102 may more generally include any source ofillumination suitable for imaging as described herein. While visiblelight embraces one useful range of wavelengths, the excitation source102 may also or instead usefully provide light near or beyond thevisible light range such as near-infrared or infrared illumination, ormore generally across any range of electromagnetic wavelengths for whichattenuation by the medium 106 can be measured. Various other embodimentsare discussed in greater detail below, and it will be appreciated thatthe term “excitation source” as used herein should be broadly understoodas any source of energy capable of achieving illumination of the object108. In one embodiment, the excitation source 102 may be a light sourcepositioned to excite a single fluorescent substance around the object108 (e.g., within the medium 106) to provide a fluorescent emission, ormore generally to illuminate the medium 106 and/or target surface 110 asrequired to capture suitable intensity measurements at the sensor 112for thickness calculations as described below.

One or more source filters 104 may optionally be employed to shape aspectral profile of the excitation source 102, such as to providenarrowband illumination from a broadband light source, or to otherwiseattenuate energy outside wavelengths of interest. For example, where thesensor 112 captures a fluorescent or other radiant image from the object108, the one or more source filters 104 may usefully remove or attenuatethe fluorescence wavelength(s) from the excitation source 102 in orderto avoid contamination of fluorescence images.

The medium 106 may include any substance, mixture, solution, compositionor the like suitable for the imaging systems and methods describedherein. In general, the medium 106 may have known and differentcoefficients of attenuation for two different wavelengths so that aratio of intensity at these wavelengths can be captured and used inthickness calculations. The medium 106 may also include a singlefluorescent, phosphorescent, or similarly radiant substance thatcontributes to the intensity of electromagnetic energy at one of the twodifferent wavelengths. In embodiments, one of the attenuationcoefficients is zero. In embodiments, one of the attenuationcoefficients is greater than or less than the other, or to improvediscrimination in a calculation including a ratio, significantly greaterthan or less than the other.

In one aspect, the medium 106 may be selected for its mechanicalproperties. Thus, the medium 106 may include one or more of a liquid, agas, a solid, a gel, or other substance or combination of substances.For example, a liquid such as a silicon oil may be conveniently employedwhere the object 108 is small and can be fit into a bath or othercontainer with the oil. As another example, a gas with a fluorescent dyemay be usefully employed in an interior space as described in variousembodiments below. In other embodiments, the medium 106 may be a castingmedium such as a curable gel into which the object 108 may be pressedand removed leaving a negative impression of the object in the medium106. In various embodiments, such a curable material may be cured whilethe object 108 is in the medium 106, after the object 108 has beenremoved from the medium 106, or some combination of these. The medium106 may cure with the passage of time, or with the application of heat,light, pressure, or the like, or through some other activation medium.

In another aspect, the medium 106 may be selected for its opticalproperties such as luminescence (e.g., fluorescence) and/or attenuation.Thus the medium 106 may in general be transparent across some portion ofthe electromagnetic spectrum so that light passing through the medium106 in some wavelengths is not attenuated. The medium 106 may also havea non-zero coefficient of attenuation at some wavelengths so that lightat these wavelengths is attenuated as it passes through the medium 106.This may be achieved, for example, through the use of an additive suchas gold nanoparticles (which can be very closely tuned to achieveattenuation at specific, narrow bands of wavelengths) or any othersubstance or combination of substances that achieves a desiredattenuation spectral profile. The medium 106 may also containfluorescent dyes, phosphorescent dyes, quantum dots, or some othersubstance or combination of substances that emits light in response toother wavelengths or other stimulus (such as an applied electricalfield, a chemical reaction, and so forth). In such embodiments, theintensity of the emitted light may be used to assist calculations of athickness of the medium 106, as described in greater detail below. Themedium 106 may also or instead include any chemiluminescent material,electroluminescent material, or other material that emits light at oneor more measurable wavelengths.

Thus, the medium 106 may in general include a variety of dyes, solutes,quantum dots, encapsulated silica nanoparticles, or other substancesthat can be combined—such as in a homogenous mixture—to provide themedium 106 with different emission properties and/or attenuationcoefficients at different wavelengths. The medium 106, includingadditives, may be formed of biocompatible materials so that it is safefor use on, in, or in close proximity to a living organism. One usefulbiocompatible dye is fluorescein sodium, although it will be appreciatedthat a variety of biocompatible fluorescent dyes are known and may beusefully employed with the systems and methods described herein.

The object 108 may be any object having a target surface 110 from whicha three-dimensional image is to be acquired. This may include, forexample biological or physiological subject matter such as teeth (or acast of teeth), bones, hands, fingerprints, or more generally anytissue, skeleton, organs, and the like including without limitationinterior surfaces such as an ear canal, nasal passage, bladder, and soforth. This may also, or instead, include fabricated items such asprecision-machined components, precision cast parts, fuel injectors,turbine blades, seals, or any other three-dimensional object wherequality control may usefully include an evaluation of three-dimensionalshape. This may also, or instead, include models that can be usefullydigitized for subsequent computerized processes such ascomputer-automated design, computer animation, and so forth. Moregenerally, the object 108 may be any object from which athree-dimensional image can be usefully captured.

The sensor 112 may include any sensor or group of sensors suitable forcapturing, in digital or electronic form, an intensity ofelectromagnetic radiation at one or more wavelengths. This may include,for example, photodiodes, charge-coupled devices (CCDs), complementarymetal oxide semiconductor (CMOS) devices, or any other optical sensor orcombination of sensors suitable for use with the systems and methodsdescribed herein. In general, the sensor 112 may be positioned tomeasure an intensity of one or more wavelengths of light in a directionof a location within a region of interest on the target surface 110,such as indicated where the optical return path 120 leaves the objecttoward the sensor 112 and sensor filter 114.

The sensor 112 may include a two-dimensional pixel array that cancapture a two-dimensional image in which a measurement at each pixellocation corresponds to an intensity of one or more wavelengths of lightin a direction within a field of view of the sensor 112. This may, forexample, include conventional CCD arrays, such as a grayscale array, ared-green-blue (RGB) array, a cyan-magenta-yellow (CMY) array, or thelike. Various techniques are known for discriminating differentwavelengths including filter masks overlaying a detector to capture aparticular range of wavelengths at each pixel location, a filter wheelwith which time-separated (and wavelength-separated) images can becaptured through each of a sequence of filters, or a prism thatseparates an optical path into three sub-paths each used to measure adifferent wavelength. In other embodiments, nested semiconductor wellsor the like may be employed to measure different wavelengths atdifferent depths within the semiconductor device. Although notseparately illustrated, it will be appreciated that the sensor 112 mayinclude a variety of camera optics such as focusing lenses, zoom lenses,prisms, mirrors, and so forth, as well as other camera hardware such asshutters, aperture controls, and so forth, any of which may be custombuilt for a particular imaging environment or integrated into acommercially-available camera or some combination of these.

In general, the techniques described herein use two measuredwavelengths. However, it should be appreciated that additionalwavelengths may be usefully employed to increase accuracy or toaccommodate use with a range of different mediums 106. The measuredwavelengths may be at or near specific wavelengths detected byconventional camera hardware, or at other wavelengths, and may ingeneral include ranges or bands of varying size around certain centerwavelengths according to the sensitivity of the sensors that are usedand/or the properties of the excitation source 102 and the medium 106.In some embodiments the measured wavelengths are 510 nanometers and 540nanometers, respectively.

The sensor filter 114 may be any filter or combination of filters usefulfor selectively passing one or more wavelengths of light to the sensor112, including the filter masks described above for discriminatingwavelengths at the sensor, or one or more filters separate from thesensor 112 for gross filtering of an incoming optical signal, such as toattenuate light outside one or more wavelengths of interest. In variousembodiments the sensor filter 114 may include a switchable opticalbandpass filter, an optical bandpass filter, a color filter, astray-light filter that attenuates all light outside of the measuredwavelengths, an excitation filter that attenuates over the excitationbands, and so on.

The computer 116 may include any suitable computing device or devicesincluding without limitation a desktop computer, laptop computer, ordedicated processing device(s). The computer may include one or moregeneral purpose or special purpose processors constructed and/orprogrammed to receive measurements of intensities, perform calculationsto determine the thickness of an attenuation medium, and output resultsof the calculations as described herein. This may include the use ofsoftware, firmware, microcode, programmable gate arrays, applicationspecific circuits, and so on. In general, the computer 116 may provideone or more high-level functions as described below.

In one aspect, the computer 116 may control operation of the excitationsource 102 and sensor 112 to obtain sensor images of the object 108.This may include supplemental functions such as controlling a supply ofthe medium 106 or otherwise providing monitoring and control of hardwarefor the systems and methods described herein. In another aspect, thecomputer may obtain data from the sensor 112, such as a two-dimensionalarray of intensity values captured from a field of view that containsthe object 108 and the medium 106. This may include intermediateprocessing such as controlling operation of the sensor 112 or a datafeed from the sensor 112, as well as processing digital measurementsfrom the sensor 112 to obtain intensity values at particular wavelengthsof interest. Thus, for example, where an RGB camera is employed, thecomputer 116 may receive three discrete wavelength measurements for eachpixel of the camera (e.g., a red wavelength, a green wavelength, and ablue wavelength) and process these RGB values at each pixel location todetermine or estimate an intensity at one or more wavelengths betweenthe discrete RGB values for use in subsequent calculations.

In another aspect, the computer 116 may calculate a thickness of themedium 106 in a direction of a location on the object 108 (e.g., alongthe optical return path 120 to a particular sensor/pixel location) basedupon a function of the intensity at two or more specific wavelengths. Ingeneral, each sensor 112 (or pixel location within a sensor 112)provides a measurement of intensity at two different wavelengths in thedirection of a location on the target surface 110, which may correspondto a general area of interest, or a particular location within a regionof interest depending on the optical resolution of the sensor 112 andrelated hardware.

Where the medium 106 has a different attenuation coefficient at each oftwo measured wavelengths and the medium 106 fluoresces or otherwiseradiates at one of these two wavelengths, the intensity at each of thetwo wavelengths can be related to a thickness of the medium 106 in thedirection of the location. Suitable adaptations may be made where, forexample, the medium 106 contains a fluorescent dye that is excited bythe excitation source 102, or where the medium 106 contains twofluorescent dyes that are excited by the excitation source 102, or wherethe medium 106 has known attenuation coefficients and the target surface110 has a known color pattern, or where the target surface 110 has aluminescent surface that luminesces at a wavelength that is attenuatedby the medium 106. In some embodiments, a baseline image of the targetsurface 110 (e.g., taken without the medium 106 present) may be used toobtain the known color pattern. Preferably, the non-absorbing medium andthe medium 106 have similar indices of refraction (i.e., they are indexmatched), so that the baseline image and any images taken with themedium 106 line up as exactly as possible. Translation, rotation,warping, and the like may also be employed to adapt a baseline image tovarious perspectives on an object, such as where a camera or othersensor obtains images from a variety of poses that are used to form acomposite three-dimensional image. However adapted, this general notionmay be employed to obtain a number of thickness measurements in thedirection of a corresponding number of locations on the target surface110

In another aspect, the computer 116 may process thickness measurementsto obtain a three-dimensional reconstruction of the target surface 110.With a number of simple constraints such as information about thephysical boundaries of the medium 106, the directionality associatedwith pixel or other sensor measurements, and a straightforwardapplication of Euclidean geometry, thickness measurements can betransformed into a three-dimensional data set representing the targetsurface 110. This three-dimensional data can be stored, displayed,output to another computer process, and so forth. It will be understoodthat while the medium 106 is depicted in FIG. 1 as having a generallyrectangular cross section, this is not strictly required and any shapeof medium 106 may be employed provided that enough information about thesurface of the medium is available to permit inferences about the targetsurface based on thickness measurements. For example, a lens of thesensor 112 may be immersed in the attenuation medium, such thatthickness measurements are made directly from a surface of the lens tothe object 108. In another aspect, the object 108 may be immersed in abath of the medium 106 where a top surface of the bath has a knownposition such that thickness can be projected (based upondirectionality) from this surface to the target surface.

This process may be supplemented in a number of ways. For example, athree-dimensional video may be created with a series of time-separatedmeasurements. In another aspect, the sensor 112 or the object 108 may bemoved (in a translation, a rotation, or some combination of these) inorder to capture a larger area of interest or the entire object 108, orin order to obtain measurements of occluded surfaces of the object 108,or for any other reason. In such a motion-based imaging process, therelative positions of the sensor 112, the object 108, and/or the medium106 may be physically tracked with motion sensors or the like, or therelative motion may be inferred using a three-dimensional registrationprocess to spatially relate successive three-dimensional data sets toone another. Regardless of the particular methodology, it will bereadily appreciated that individual spatial measurements, or groups ofspatial measurements, may be combined to form a larger three-dimensionalmodel, and all such techniques that would be apparent to one of ordinaryskill in the art for creating a three-dimensional reconstruction areintended to fall within the scope of this disclosure.

In another aspect, the computer 116 may provide a user interface forcontrol and operation of the system 100, as well as tools for displayingthickness measurements, displaying or manipulating reconstructedthree-dimensional models, and so forth.

The computer 116 may also support calibration of the system 100 in orderto correct for, e.g., variations in the sensor 112, the excitationsource 102, and related optics, or variations in concentration ofadditives to the medium that absorb, scatter, attenuate, fluoresce, orotherwise impart various optical properties to the medium. For exampleand without limitation, it will be understood that one can characterizethe sensor 112 using a calibration fixture or the like, prior toemploying the sensor 112 in the system 100. Additionally, it will beunderstood that by taking controlled measurements of the absorptionspectrum or the emission spectrum for the medium 106 it may be possibleto improve the accuracy of the thickness measurements and relatedcalculations. Calibration may, for example, include the use of an object108 having a known shape and a known position within the medium 106, orthe use of a container for the medium having a known shape. A variety ofsuitable calibration techniques will be readily appreciated based uponthe use of known shapes, dimensions, surface patterns, and so forth, anyof which may be adapted to use with the imaging systems describedherein.

A supply 122 of the medium 106 may be provided and adapted to distributethe medium 106 between the sensor 112 and the target surface 110. Itwill be understood that, while the supply 122 is depicted as an externalreservoir, the supply should more broadly be understood as anystructures that deliver the medium 106 and/or retains the medium 106about the object 108 in a manner that permits thickness measurementsincluding any pumps, valves, containers, drains, tubing, and the likeconsistent with supplying the medium 106 for the uses described herein.

FIG. 2 shows the emission and absorption spectra for fluorescein sodium.In general, the imaging techniques described above may employ knownERLIF techniques using two different fluorescent dyes. However, in oneaspect the imaging system may instead be implemented using a medium thatcontains a single fluorescent dye (or other substance) such asfluorescein sodium that has an absorption spectrum 202 that overlapswith an emission spectrum 204. By exciting this dye with a blue lightand capturing fluorescent image pairs in ten nanometer bands within theoverlapping spectrum 206 of non-zero absorption and attenuation, such ascentered on about 510 nanometers and about 540 nanometers, intensityvalues can be obtained for thickness calculations in a manner similar tothe ERLIF techniques noted above. Thus in one embodiment there isdisclosed herein a thickness measurement and/or three-dimensionalimaging system that uses a medium with a single fluorescent dye, whereinthe dye has overlapping, non-zero emission and absorption spectra.

FIG. 3 shows a three-dimensional imaging system using a luminescentsurface applied to an object. In general, the system 300 may be asdescribed above with reference to FIG. 1 with differences as notedbelow. A luminescent layer 322 may be applied to the target surface 110of the object 108, and may emit light at a first wavelength and a secondwavelength that can be measured by the sensor 112 in order to facilitatecalculations of thickness of the medium 106. In general, the sensor 112may be positioned to capture an intensity of the first wavelength andthe second wavelength in a direction of a location on the target surface110, and a processor such as the computer 116 may be programmed tocalculate a thickness of the medium in the direction of the locationbased upon a function of the intensity of the first and secondwavelengths.

In one aspect, a luminescent layer 322 is applied to the target surface110 or embedded within the object 108 (such as using a waveguide or thelike). Emissions from the luminescent layer 322 may travel along theoptical return path 120 as described above. Although the followingdescription refers explicitly to a layer of luminescent material, itwill be readily understood that the object 108 may also or instead befabricated from a luminescent material to achieve a similar effect, ormay contain waveguides or the like that luminesce. Thus as used hereinthe term “luminescent layer” should not be interpreted as requiring adiscrete layer of luminescent material on the target surface 110 of theobject 108. Rather any technique for rendering the object 108luminescent should be understood as creating the luminescent layer 322as that term is used herein unless a different meaning is explicitlystated or otherwise clear from the context. In general, the luminescentlayer 322 may be formed of any suitable combination of materialsselected for appropriate mechanical properties, optical properties, andother properties.

Mechanical properties of the luminescent layer 322 may depend on themanner in which the luminescent layer 322 is to be applied. For example,an oil or other relatively viscous material may be appropriate for dipcoating the object 108, while a less viscous fluid might be usefullyemployed for spraying or painting onto the target surface 110. In otherembodiments, a thin film or other membrane may be impregnated with aluminescent material (or fabricated from a luminescent material, orcoated with a luminescent material) and be used to form the luminescentlayer 322 in an inflatable membrane as described below. The membrane maybe elastic, deformable, flexible, pliable, or any combination of these,or have any other properties useful for forming a conforming,luminescent layer over the object 108.

In embodiments, the luminescent layer 322 may be a membrane that can bewrapped around some or all of the object 108. The object 108, enclosedin the luminescent layer 322 may then be introduced into the medium 106and thickness measurements may be obtained from any number of poses fromwithin or outside of the medium 106. Thus for example, where the object108 is a human foot, a sock may be fashioned of a material with theluminescent layer 322 disposed on an outside of the sock. A foot maythen be inserted into the sock, which may in turn be placed into themedium 106 to obtain a three-dimensional model of the foot. Thisapproach may more generally be employed to obtain three-dimensionalimages using a membrane such as any of the elastic or inelasticmembranes described herein as an exterior enclosure for a targetsurface. Thus in one embodiment there is disclosed herein a sock (orother enclosing membrane) with a luminescent exterior surface, which maybe used for capturing three-dimensional images of an object insertedinto the sock.

Optical properties of the luminescent layer 322 may be controlled by theintroduction of suitable additives. The luminescent layer 322 mayinclude a fluorescent dye or other radiant substance that responds toillumination from the excitation source 102. One suitable fluorescentsubstance may include coumarin-153, which is a powder that can dissolveand/or spread very well in certain plastics, has suitable fluorescentproperties, and appears to be non-toxic. In another aspect, theluminescent layer 322 may contain a chemiluminescent orelectroluminescent material that serves as a direct source of light.Suitable chemiluminescent materials may include a solution with hydrogenperoxide in the presence of a catalyst (e.g., iron or copper), cyalumein a solution with hydrogen peroxide in the presence of a catalyst(e.g., sodium salicylate), and so on. It will be appreciated that avariety of liquid-phase and gas-phase chemiluminescent compositions ofmatter may be employed. Suitable electroluminescent materials may, forexample include powder zinc sulfide doped with copper or silver, thinfilm zinc sulfide doped with manganese, and so on. More generally, avariety of chemiluminescent and electroluminescent materials are knownand may be adapted to use as a luminescent layer 322 as describedherein. Thus, the luminescent layer 322 may include a chemiluminescentlayer, an electroluminescent layer, a fluorescent layer, or somecombination of these.

In alternate embodiments, the luminescent layer 322 may include anoptical waveguide on the target surface 110 or within the object 108. Itwill be understood that a variety of geometries, mode structures, andmaterials for the optical waveguide are possible and may be adapted touse with the systems described herein.

The excitation source 102 may provide one or more wavelengths of lightto excite a fluorescent dye or the like within the luminescent layer322. In other embodiments, the excitation source 102 may be entirelyomitted, or may be alternatively realized as a chemical, electrical, orother source of energy that produces illumination from the luminescentlayer 322. In embodiments, the excitation source 102 may include anelectrical power source that directly powers a waveguide in the object108. In other embodiments, the excitation source 102 may include anelectrical field, chemical precursor, or other means for illuminatingthe luminescent layer 322.

Thus it will be appreciated that the luminescent layer 322 may be formedof a variety of different carriers and additives. In embodiments, theluminescent layer 322 may contain any suitable luminescent pigment, suchas a fluorescent dye in a liquid carrier that can be sprayed or paintedonto the object 108, or a film or membrane that is coated or impregnatedwith a fluorescent material. For in vivo imaging, the luminescent layer322 may be formed of biocompatible substances. In embodiments, theluminescent layer 322 may include biocompatible fluorescent metal oxidenanoparticles (and coatings containing same), thin film flexibleelectroluminescent sources, or nanoparticles with a surface coating ofchemiluminescent molecules.

In embodiments with a luminescent layer 322, suitable intensitymeasurements may be obtained for thickness calculations based uponrelative attenuation of different wavelengths without the need for afluorescent or otherwise luminescent medium 106. In order to achievedesired attenuation properties, the medium 106 may include a carrierformed of a transparent fluid in which gold nanoparticles or nanorodsare uniformly distributed. Gold nanoparticles or nanorods have anabsorption profile that can be tuned based on the size and shape of thenanoparticles or nanorods themselves. In embodiments, the goldnanoparticles or nanorods can be tuned to absorb more optical energywithin a predetermined band of visible light wavelengths than at otherwavelengths. The gold nanoparticles or nanorods may have a concentrationwithin the carrier such that the medium 106 is transparent (i.e.,maintains substantially zero attenuation) outside of the predeterminedband.

It will be appreciated that disclosed herein are various means forperforming the functions associated with the use of the luminescentlayer 322. An applying means for applying the luminescent layer 322 tothe target surface 110 may include, for example, a paint brush, asprayer, an atomizer, or a bath of material for the luminescent layer322 into which the target surface 110 may be dipped. A distributingmeans may include a supply of the medium as well as any structures forretaining the medium in a desired area around the object such as acontainer with side wall for a liquid, or a gas-tight chamber forretaining the medium in a gaseous form. Sensor means may include any ofthe sensors described herein. A processing means may include any of thecomputing devices or other processing hardware described herein.

FIG. 4 shows a three-dimensional imaging system using a passive opticallayer applied to an object. In general, the system 400 is as previouslydescribed with differences as noted below. A passive layer 422 may beapplied to the target surface 110 of the object 108 in order to impartthe object 108 with known optical properties that can be used incombination with an attenuating medium 106 to determine thickness basedupon measurements of intensity at various wavelengths.

The medium 106 may be any one or more of the attenuating media describedabove that provide different attenuation coefficients for at least twodifferent wavelengths. The excitation source 102 may be a broadbandlight source that provides illumination of the object 108 over a rangeof wavelengths (or ranges of wavelengths) that includes the at least twodifferent wavelengths used for thickness calculations.

In general, the passive layer 422 may be constructed using any of thetechniques described above for a luminescent layer 322. This includesspraying, painting, or otherwise applying the passive layer 422 to theobject 108, or fabricating the object 108 with an exterior surfacehaving the desired properties. In general, the passive layer 422 impartsa known optical pattern onto the object 108 so that the object 108 has apredetermined color over a region of interest. The predetermined colormay be a uniform color that is unknown, a uniform color that is a known(e.g., a specific color), or a known color distribution.

In operation, the object 108 may be illuminated by the excitation source102, and an intensity at the at least two wavelengths may be measured bythe sensor 112. By using a broadband light source and a known colordistribution on the object 108, the ratio of reflected intensities canbe assumed to be constant across the target surface 110. Thus anyvariation in the ratio of measured intensities can be correlated to athickness of the attenuating medium 106 and a thickness can becalculated. Using a ratio may also reduce the effects on thicknesscalculations of any spatial non-uniformity in the illumination source orin the reflectivity of the passive layer.

In one aspect, the passive layer 422 may have a color that varies. Thismay be useful, for example, where the target surface 110 is expected toexhibit significant variability in height (with correspondingvariability in thickness of the medium 106). In general, the sensitivityof measured intensities of light at the sensor 112 to the thickness ofthe medium 106 may depend on a number of factors including a colorselected for the passive layer 422. Where a surface is expected to benearly planar, high sensitivity may be preferred in order to achievegreater resolution in thickness measurements. However, where a surfaceis expected to be highly non-planar, lower sensitivity may be requiredin order to avoid saturation of the sensor 112, or more generally toprovide an adequate depth of field to capture depth. Where someinformation is available a priori concerning the shape of the object 108being measured, this information can be used to scale measurementresolution accordingly with a suitable, corresponding selection of coloron the target surface 110.

The passive layer 422 may also or instead have other properties selectedto assist in capturing accurate thickness measurements. For example, amatte finish may provide more consistent reflective properties for thetarget surface 110 across a range of illumination conditions. Similarly,a dark color finish may absorb certain wavelengths of incident lightthat would otherwise interfere with sensor measurements.

In one aspect, a system described herein for capturing thicknessmeasurements from a target surface with a known color distribution mayinclude a distributing means, which may be the supply 122 or any of theother means described above for distributing a medium between a targetsurface and a sensor or retaining the medium in this distribution. Thesystem may include an illuminating means which may be any of the lightsources or other excitation sources described above. The system mayinclude a sensor means which may include any of the sensors describedabove suitable for capturing wavelength intensity data corresponding tothe illumination provided by the illumination means. Finally, the systemmay include a processing means which may include any processor orcomputing device described herein programmed to calculate thicknessbased on wavelength intensity measurements and, where appropriate, tofurther reconstruct a three-dimensional image from the resultingthickness(es).

In one aspect, the systems described above advantageously permitthree-dimensional imaging using a single camera such as a conventionalcolor camera. By physically arranging a medium, illumination sources,and/or surface treatment of an object according to the variousembodiments described above, thickness measurements can be obtained witha single camera and geometrically converted into a three-dimensionalimage of a target surface. Thus, in one aspect a three-dimensionalimaging device disclosed herein includes a camera and a processor. Thecamera, which may be a conventional color camera, may include a lens andone or more sensors capable of capturing a two-dimensional color imageof a field of view including an intensity at a first wavelength and asecond wavelength, which may be any of the wavelengths or bands ofwavelengths described above. The intensity at each pixel location in thetwo-dimensional image corresponds to a direction from the lens into thefield of view so that suitable directionality for the measurement can beinferred and employed in a three-dimensional reconstruction. Theprocessor, which may be the computer or any other processing devicesdescribed above, may then calculate a thickness of a medium in thedirection corresponding to each one of the plurality of pixel locationsas a function of the intensity of the first wavelength and the intensityof the second wavelength at that one of the plurality of pixellocations, thereby providing a plurality of thickness measurements. Fromthis plurality of thickness measurements and related information such asthe directionality associated with each pixel and any a prioriinformation about the geometric boundaries of the medium, the processormay calculate a three-dimensional image of an object within the field ofview.

It should be appreciated that the presently disclosed use of a singlecamera in obtaining a three-dimensional image can be applied in thecontext of conventional ERLIF technique as well.

For sensors 112, the camera may include a complementary metal oxidesemiconductor (CMOS) chip camera with one or more CMOS sensors in asolid state device, or the camera may include an array of charge-coupleddevices in a solid state device. The camera may include any number offilters to selectively capture the intensity of the first and secondwavelengths at each one of the plurality of pixel locations. The filtersmay include a filter mask disposed on the imaging device (i.e.,integrated into the camera chip or other solid state imaging device).For example, the camera may include a plurality of filters forselectively capturing an intensity of different wavelengths at differentones of the plurality of pixel locations, such as a conventional RGB orCMY filter mask, or a plurality of filters to selectively capturespecific wavelengths used in thickness calculations. The filters mayalso or instead include external filter devices or systems, and mayinclude active filters that permit adjustments to filter propertiesduring operation or fixed filters such as dichroic mirrors or the likemanually positioned in front of a camera lens.

The camera may capture RGB (red, green, blue) or CMY (cyan, magenta,yellow) color images as typically found in commercially-availablehardware, or any other useful narrow or broad ranges of wavelengths. Inone embodiment where the medium is a gas, the camera may be immersed inthe gas along with the target surface and the thickness measurement maybe an entire distance from the camera lens to a location on the surfaceof the object. A light source or other excitation source may also beincluded, all as generally described above, and the light source mayinclude any filter or combination of filters suitable for a particularmedium. Such filters may be useful, for example, to selectively pass oneor more wavelengths to excite a fluorescent material, or to attenuatelight in wavelengths where fluorescent light is emitted so as to avoidinterference with fluorescent emissions from the target surface or theintervening medium.

In another aspect, useful mediums are disclosed for use with the imagingsystems described above. In general, these mediums include anycombination of carriers and other substances (for attenuation or forfluorescence) devised specifically for use with the systems above andnot otherwise commercially available or described in the art.

For example, in one aspect, a composition of matter described hereinincludes a carrier formed of a transparent fluid medium and a pluralityof gold nanoparticles uniformly distributed within the carrier. The goldnanoparticles may be advantageously tuned to absorb optical energywithin a predetermined band of visible light wavelengths in order tofacilitate thickness measurements and three-dimensional imaging asdescribed herein.

The plurality of gold nanoparticles may be tuned using a shape of theplurality of gold nanoparticles and/or the plurality of goldnanoparticles may be tuned using a size of the plurality of goldnanoparticles. The plurality of gold nanoparticles may have aconcentration within the carrier such that the composition has zeroattenuation outside the predetermined band. The predetermined band maybe between 450 nanometers and 550 nanometers. The carrier may be one ormore of an oil, a gel, a gas, and a liquid, any of which might usefullybe selected according to the subject matter being imaged and the imagingtechnique being employed. In one aspect, the carrier may include asilicon oil. In another aspect where the subject matter can be cast, ora gel might otherwise serve as a useful medium, the carrier may includea glycerol, or more generally any gelatin, glycerol, and varioussolutions or other formulations or preparations of same, or any othersubstance or combination of substances with similar properties. In otherembodiments, the carrier may be curable. The carrier may include apolymer, blend of polymers, or any other curable substances that can beconformed to a target surface and then cured using, e.g., chemicalcuring, heat curing, light curing, time curing, and so forth. Thecarrier may also be biocompatible so that it can be safely used for invivo imaging of subject matter such as human dentition or a human earcanal.

In another aspect, the medium may include a carrier formed of atransparent fluid medium and a dye that is uniformly distributed withinthe carrier. The dye may consist of a single fluorescent dye having anabsorption spectrum over which the dye absorbs light and an emissionspectrum at which the dye fluoresces, wherein the absorption spectrumand the emission spectrum have at least one overlapping non-zero region.This single-dye formulation improves upon carriers used in, e.g.,conventional ERLIF by reducing to one the number of fluorescent dyesrequired in the medium. By adapting the imaging hardware and developinga suitable mathematical approach, the applicants have devised atechnique for capturing images with a medium that contains a singlefluorescent dye. Thus it should be appreciated that in this context anyreference to a single dye, single fluorescent dye, single fluorescentsubstance, or the like is intended to refer to exactly one fluorescentsubstance, that is, one and only one fluorescent substance and no morethan one fluorescent substance, which marks a significant departure fromand improvement upon previous ERLIF imaging techniques.

The carrier may be one or more of an oil, a gel, a gas, and a liquid.For example, the carrier may include a silicon oil or a glycerol. Thedye may be fluorescein sodium. The carrier may be curable, as generallydiscussed above, and the carrier may be biocompatible. In oneembodiment, the dye may be encapsulated in silica nanoparticles. Thecomposition may have an absorption spectrum including a peak within avisible light, which may be a local maximum or an absolute maximum. Thecomposition may similarly have an emission spectrum including a peakwithin a visible light range.

FIG. 5 is a flow chart of a method for three-dimensional imaging using aluminescent layer applied to a target surface of an object.

The method 500 may begin with applying a luminescent layer to a targetsurface as shown in step 502. The luminescent layer, which may be afluorescent layer, a chemiluminescent layer, an electroluminescentlayer, and so forth, may be applied using any of the techniquesdescribed above including spraying, painting, dip-coating and so forth,or by fabricating the object from a fluorescent material. For example,this may include applying a fluorescent layer to the target surface as afluorescent pigment in a liquid carrier. The luminescent layer may emitlight at a first wavelength and a second wavelength, such as in responseto any of the excitation sources or other stimuli described above. Inother embodiments, the luminescent layer may emit light at a firstwavelength, such as due to fluorescence, and reflect light at a secondwavelength, where the first wavelength and the second wavelength areused to obtain thickness measurements of a surrounding medium.

As shown in step 504, the method 500 may include distributing a mediumsuch as any of the media described above between the luminescent layerand a sensor. It will be appreciated that this may include a variety oftechniques for interposing a medium between the object and the sensor,such as pouring the medium in liquid form into a container with theobject, immersing the object in the medium, or supplying a gas into achamber with the object. In another aspect, this may include inflating aballoon, bladder, or other inflatable membrane with a gas that containsa fluorescent dye, and then inserting the sensor into the inflatablemembrane. In another aspect, this may include inserting an object into asock or other enclosure before distributing the medium as describedabove.

In some embodiments a balloon or the like containing the medium may bepushed against, placed upon, or otherwise brought into contact with anobject so that it conforms to a target surface. The interior of aballoon in this posture may be used to obtain a three-dimensionalimpression of the target surface against the balloon using any of thetechniques described herein. Thus it will be appreciated that techniquesdescribed herein for measurement of interior cavities may also orinstead be adapted to measurements of any surface. In one aspect, adevice deploying the inflatable membrane may be specifically adapted tothis purpose, such as by inflating a membrane within a cone (which mayalso form a sealed interior along with the membrane) or at the end of asupporting handle that facilitates placement of the inflatable membraneagainst an object.

As shown in step 506, the method 500 may include exciting theluminescent layer so that it provides some combination of reflectedlight and/or radiant light. As discussed above, this may include one ormore wavelengths of light from an excitation source that are reflectedoff the target surface and/or one or more wavelengths of light radiatingfrom the luminescent layer due to fluorescence, electroluminescence,chemiluminescence, or any other suitable mechanism so that theluminescent layer emits light as described in step 502. The luminescentlayer may include a fluorescent layer that emits light at the firstwavelength and the second wavelength in response to an excitation lightsource, so that exciting the luminescent layer as described hereinincludes exciting the fluorescent layer with the excitation light sourceto provide a fluorescent emission from the fluorescent layer. Theluminescent layer may be excited with an excitation source such as abroadband light source or any other light source that provides light atone or more wavelengths other than the first wavelength and the secondwavelength. The excitation light source may also or instead include oneor more lasers, one or more light emitting diodes, an incandescent lamp,and so forth. In another aspect, a waveguide may be built into theobject or target surface and serve directly as the luminescent layer.

As shown in step 508, the method 500 may include measuring an intensityof the first wavelength and an intensity of the second wavelength in adirection of a location on the target surface with the sensor, which mayfor example be any of the sensors described above.

As shown in step 510, the method 500 may include determining a thicknessof the medium in the direction of the location based upon a function ofthe intensity of the first wavelength and the intensity of the secondwavelength. It will be understood that the actual relationship betweenwavelength intensities and thickness may depend on a variety of factorssuch as the nature of the luminescent layer, the coefficient ofattenuation of various wavelengths by the medium, an intensity of theexcitation source, and so forth. Where the sensor provides measurementsfrom a plurality of pixel locations (corresponding to a plurality oflocations on the target surface), a two-dimensional array of suchintensity measurements may be used to obtain a two-dimensional array ofthickness calculations.

A more detailed analytical development of calculating or determiningthickness using a fluorescent surface is now provided. The fluorescencecharacteristics of a target surface and the characteristics of theabsorbing medium may be chosen so that a part of the fluorescencespectrum is absorbed more than other parts of the fluorescence spectrum.For example, where two intensity bands (also referred to herein simplyas intensities) centered on wavelengths λ₁ and λ₂ are measured, themedium's absorptivity coefficients ε_(λ1) and ε_(λ2) should bedifferent. Where a band centered around λ₁ is the preferentiallyabsorbed band, then ε_(λ1)>ε_(λ2). The normalized measured intensitiesof both wavelength bands traveling from the fluorescent surface to animage sensor located a distance d within the medium (or d through themedium for a sensor outside the medium) and away from the surface may bedescribed by the following equations:

$\begin{matrix}{{\overset{\_}{I_{\lambda 1}}(d)} = {\frac{I_{\lambda 1}(d)}{I_{{\lambda 1},{x = 0}}} = ^{{- ɛ_{\lambda 1}}{Cd}}}} & \left\lbrack {{Eq}.\mspace{14mu} 1} \right\rbrack \\{{\overset{\_}{I_{\lambda 2}}(d)} = {\frac{I_{\lambda 2}(d)}{I_{{\lambda 2},{x = 0}}} = ^{{- ɛ_{\lambda 2}}{Cd}}}} & \left\lbrack {{Eq}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

The intensity of the bands at the fluorescent surface, I_(λ1,χ=0) andI_(λ2,χ=0), is dependent purely on the fluorescence properties of thesurface and the spectrum and intensity of the excitation illumination.Though variations in excitation intensity may change the intensity ofthe fluorescence at the surface, any change in the ratio of I_(λ1,χ=0)and I_(λ2,χ=0) will be negligible. Therefore, one can take the ratio ofthe normalized intensities from [Eq. 1] and [Eq. 2] above and obtain anexpression that is solely dependent on depth and the concentration andabsorption coefficients of the medium:

$\begin{matrix}{{I_{Ratio}(d)} = {\frac{\overset{\_}{I_{\lambda 1}}(d)}{\overset{\_}{I_{\lambda 2}}(d)} = ^{\lbrack{{({ɛ_{\lambda 2} - ɛ_{\lambda 1}})}{Cd}}\rbrack}}} & \left\lbrack {{Eq}.\mspace{14mu} 3} \right\rbrack\end{matrix}$

Conspicuously, the intensity ratio decreases exponentially as thedistance through the medium increases. This relationship permits acalculation of thickness through the medium. It will be appreciated thatin practice, actual measurements may be obtained and fit to thisrelationship using any suitable techniques in order to providecalibrated thickness measurements from a working system.

As shown in step 512, the method 500 may include reconstructing athree-dimensional image of the target surface. This may include, forexample constructing a three-dimensional image of the region of interestwith a plurality of measurements from the sensor using any of a varietyof geometric constraints along with thicknesses of the medium ascalculated from intensity measurements. The geometric constraints mayfor example include any spatial information about boundaries of themedium, such as at least one known surface of the medium that can becombined with one or more thickness measurements (and a direction forsame) to derive a surface point on the target surface. It will beappreciated that the at least one known surface may be any of a varietyof surfaces in the various embodiments discussed herein where spatialinformation about the surface (or more specifically, the surface-mediumboundary) is known. Thus for example, a known surface may be an exposedtop surface of a tank that contains the medium in a liquid form, or aninterior side surface or bottom surface of a transparent container ofthe medium. The known surface may also or instead include a camera lensor other optical element that separates sensors from a gaseous medium.More generally, any spatial boundary of the medium that is known or canbe measured may serve as the at least one known surface used inthree-dimensional reconstruction as described in the various methods andsystems herein. In addition, any number of three-dimensional images maybe combined through registration or the like to form a compositethree-dimensional image of some or all of the target surface.

It will be understood that numerous variations to the above method 500are possible, including variations adapted to particular imagingtechniques. For example, where a gas is used as a medium, the method 500may include providing a transparent barrier between the target surfaceand the sensor to retain the gas against the target surface. Forexample, the object may be placed in a transparent, gas-tight chamberand filled with a fluorescent gas. By using thickness measurements takenfrom outside of the chamber, along with information about the interiordimensions of the chamber, a three-dimensional reconstruction of atarget surface on the object may be obtained as generally describedabove. In another aspect, the method 500 may include immersing thetarget surface in a liquid and positioning the sensor above a topsurface of the liquid for capturing light intensity measurements. Insuch embodiments, the position of the top surface of the liquid may bereadily determined and used as a basis for converting thicknessmeasurements into a three-dimensional reconstruction.

More generally, it will be appreciated that the method 500 describedabove is set forth by way of example and not of limitation. Numerousvariations, additions, omissions, and other modifications will beapparent to one of ordinary skill in the art, and all such modificationsare intended to fall within the scope of this disclosure. In addition,the order or presentation of these steps in the description and drawingsis not intended to require this order of performing the recited stepsunless a particular order is expressly required or otherwise clear fromthe context.

Thus for example, a luminescent layer may be applied to a target beforeor after a medium is distributed between the target and a sensor,depending upon the manner in which this layer is applied. As anotherexample, the medium may be distributed between a target and sensor, orthe target may be immersed in a tank of the medium in liquid form, whichachieves the same purpose of placing the medium against the surface forpurposes of accurate thickness measurements. As another example, thismay include inserting a camera into a container of liquid with thetarget, in which case a thickness measurement may begin at the cameralens. As another example, this may include providing other boundaryinformation for the medium, such as a liquid surface location, atransparent barrier location through which the medium may be measured,and so forth. As another example, exciting the luminescent layer mayinclude activating a luminescent layer on the surface throughfluorescence, phosphorescence, electroluminescence, chemiluminescence,and so forth.

FIG. 6 is a flow chart of a method for three-dimensional imaging using asingle fluorescent dye.

As shown in step 602, the method 600 may include distributing a mediumbetween a target surface and a sensor, the medium including a singlefluorescent substance having a fluorescence emission spectrum thatoverlaps in wavelength with a non-zero absorption spectrum of themedium. The medium may, for example, have zero absorption at the secondwavelength. The single fluorescent substance may be fluorescein sodium,which has emission and absorption spectra as illustrated above. Usingthis or a similar fluorescent substance, the first wavelength may beabout 510 nanometers and the second wavelength may be about 540nanometers. In another embodiment, the single fluorescent substance mayinclude quantum dots or other scintillants that radiate in response toincident electromagnetic radiation. In various embodiments, the mediummay include a liquid, a gas, a solid, and/or a gel, with suitableadaptations to the associated hardware. For example, where the medium isa gas, the method 600 may include providing a transparent barrier orother enclosure as described above. Where the medium is a liquid, themethod 600 may include immersing the target surface in the liquid andpositioning the sensor above the liquid.

As shown in step 604, the method 600 may include exciting the singlefluorescent substance to provide a fluorescent emission, such as bydirecting a broadband light source or a light emitting diode(s) towardthe fluorescent dye and/or in the direction of the target surface.

As shown in step 606, the method 600 may include measuring thefluorescent emission with the sensor in a direction of a location on thetarget surface, including measuring an intensity at a first wavelengthand an intensity at a second wavelength, wherein the medium has adifferent coefficient of attenuation for the first wavelength and thesecond wavelength. Where a conventional camera or other sensor devicehaving a two-dimensional pixel array is employed, measuring thefluorescent emission may include measuring the intensity of the firstwavelength and the intensity of the second wavelength from a pluralityof locations on the target surface at a corresponding plurality of pixellocations within the sensor, thereby providing a two-dimensional arrayof thickness measurements.

As shown in step 608, the method 600 may include determining a thicknessof the medium in the direction of the location based upon a function ofthe intensity of the first wavelength and the intensity of the secondwavelength. This may include, for example, calculating a ratio of theintensity of the first wavelength to the intensity of the secondwavelength.

For the case where three-dimensional imaging is performed using a mediumcontaining a fluorescent substance whose absorption and emission spectraoverlap, thickness can be measured by taking the intensity ratio of twofluorescent bands centered around wavelengths λ₁ and λ₂, so long as themedium self-reabsorbs one of the fluorescent bands preferentially overthe other. Supposing that only the band centered around λ₁ undergoesself-reabsorption, then ε_(λ1) is some finite positive value andε_(λ2)≈0.

At any point a distance x from the sensor (or a distance χ into themedium), the excitation illumination intensity I_(e) (χ) is given by:

I _(e)(χ)=I _(o) e ^(−ε) ^(λe) ^(Cχ)  [Eq. 4]

where I₀=I_(e)(O) is the excitation intensity at the sensor location andε_(λe) is the absorption coefficient of the medium at the excitationwavelength λ_(e).

The fluorescent emissions contributed by a differential element withinthe medium in the two bands centered around wavelengths λ₁ and λ₂ aregiven by:

dI _(ƒ1) =I _(e)(χ)ε_(λe) CΦη ₁ dχ  [Eq. 5]

dI _(ƒ2) =I _(e)(χ)ε_(λe) CΦη ₂ dχ  [Eq. 6]

where Φ is the medium's quantum efficiency, or ratio of the energyemitted to the energy absorbed, and η₁ η₂ are the relative emissions ofthe medium at the two wavelengths λ₁ and λ₂. If ε_(λ1)>0 and ε_(λ2)≈0,the first wavelength band will undergo absorption while the second bandwill not. Where the excitation illumination intensity is much greaterthan any fluorescent emission, any intensity increase in both thereabsorbed and the non-reabsorbed wavelength bands can be neglected.Consequently, the differential fluorescence intensity equationsincluding the reabsorption of the λ₁ band can be written as:

dI _(ƒ1) =I _(o) e ^(−ε) ^(λe) ^(Cχ)ε_(λe) CΦη ₁ e ^(−ε) ^(λ1) ^(Cχ)dχ  [Eq. 7]

dI _(ƒ2) =I _(o) e ^(−ε) ^(λe) ^(Cχ)ε_(λe) CΦη ₂ dχ  [Eq. 8]

To calculate the fluorescent intensities a distance d from the sensor(or through the medium in a particular direction from the sensor, theseequations may be integrated from x=0 to x=d:

$\begin{matrix}{{I_{f\; 1}(d)} = \frac{I_{o}ɛ_{\lambda \; e}{{\Phi\eta}_{1}\left\lbrack {1 - ^{{({{- ɛ_{\lambda \; e}} - ɛ_{\lambda \; 1}})}{Cd}}} \right\rbrack}}{ɛ_{\lambda \; e} + ɛ_{\lambda \; 1}}} & \left\lbrack {{Eq}.\mspace{14mu} 9} \right\rbrack \\{{I_{f\; 2}(d)} = {I_{o}{{\Phi\eta}_{2}\left\lbrack {1 - ^{{- ɛ_{\lambda \; e}}{Cd}}} \right\rbrack}}} & \left\lbrack {{Eq}.\mspace{14mu} 10} \right\rbrack\end{matrix}$

The ratio of the two fluorescence measurements may be taken to obtain arelationship between depth and the measured wavelengths:

$\begin{matrix}{{I_{Ratio}(d)} = {\frac{I_{f\; 1}(d)}{I_{f\; 2}(d)} = \frac{ɛ_{\lambda \; e}{\eta_{1}\left\lbrack {1 - ^{{({{- ɛ_{\lambda \; e}} - ɛ_{\lambda \; 1}})}{Cd}}} \right\rbrack}}{{\eta_{2}\left\lbrack {1 - ^{{- ɛ_{\lambda \; e}}{Cd}}} \right\rbrack}\left( {ɛ_{\lambda \; e} + ɛ_{\lambda \; 1}} \right)}}} & \left\lbrack {{Eq}.\mspace{14mu} 11} \right\rbrack\end{matrix}$

This relationship permits a calculation of thickness through the medium.It will be appreciated that in practice, actual measurements may beobtained and fit to this relationship using any suitable techniques inorder to provide calibrated thickness measurements from a workingsystem.

As shown in step 610, the method 600 may include constructing athree-dimensional image of a region of interest with a plurality ofmeasurements from the sensor using any of a variety of geometricconstraints such as known boundaries of the medium or a containertherefore along with thicknesses of the medium as calculated fromintensity measurements. In addition, a number of such three-dimensionalimages may be combined through registration or the like to form athree-dimensional image of some or all of the target surface.

It will be appreciated that the method 600 described above is set forthby way of example and not of limitation. Numerous variations, additions,omissions, and other modifications will be apparent to one of ordinaryskill in the art. In addition, the order or presentation of these stepsin the description and drawings is not intended to require this order ofperforming the recited steps unless a particular order is expresslyrequired or otherwise clear from the context. Thus, for example, afluorescent or other luminescent surface may be excited before a mediumis distributed between a target and a sensor, or a phosphorescentsubstance may be readily substituted for the fluorescent substance. Allsuch modifications are intended to fall within the scope of thisdisclosure, which should be interpreted in a non-limiting sense.

FIG. 7 is a flow chart of a method for three-dimensional imaging basedupon absorption. In this method 700, a predetermined color on the targetsurface is used in combination with a broadband light source to obtain areflection at two different wavelengths, one of which is attenuated moreby an intervening medium than the other. A variety of predeterminedcolors may be used. For example, the color may be a specific color(e.g., blue), or the color may be unknown provided it is uniform overthe target surface. In other embodiments, a known color distribution maybe used, such as to provide different measurement scaling or gain.

As shown in step 702, the method 700 may begin with distributing amedium between a target surface and a sensor, the target surface havinga predetermined color over a region of interest, which may be any areawithin a target surface of an object. The medium may be characterized bya first attenuation coefficient at a first wavelength and a secondattenuation coefficient different from the first attenuation coefficientat a second wavelength. The first attenuation coefficient may be zero,or more generally any value less than the second attenuationcoefficient.

The sensor may be any of the sensors described above suitable forcapturing an intensity at the first wavelength and the secondwavelength. In one aspect, the sensor may be a CCD array or the likethat measures the intensity of the first wavelength and the intensity ofthe second wavelength from a plurality of locations within the region ofinterest at a corresponding plurality of pixel locations within thesensor, thereby providing a two-dimensional array of thicknessmeasurements.

In one aspect, the medium may be any of the media described above, suchas a solid, a liquid, a gel, or a gas. The medium may include anysubstance or combination of substances that results in differentcoefficients of attenuation at the first and second wavelengths. Wherethe medium is a gas, the method 700 may include providing a transparentbarrier between the target surface and the sensor to retain the gasagainst the target surface. Where the medium is a liquid, the method 700may include immersing the target surface in the liquid and positioningthe sensor above a top surface of the liquid.

As shown in step 704, the method 700 may include illuminating a locationin the region of interest, such as with a broadband light source, alaser, one or more light emitting diodes, or more generally, anyexcitation source capable of illuminating the location in a manner thatpermits a capture of reflected wavelengths at the sensor. In anotheraspect, illuminating the location may include illuminating with one ormore of a chemiluminescent substance, an electroluminescent substance,and an optical waveguide in the target surface. Where the source ofillumination is disposed on the target source or within the object, itwill be appreciated that this source may itself impart the predeterminedcolor upon which thickness calculations are based.

As shown in step 706, the method 700 may include measuring an intensityof the first wavelength and an intensity of the second wavelength in adirection of the location with the sensor. The method 700 may includefiltering one or more wavelengths of light between the medium and thesensor, such as by using any of the sensor filters described above. Themethod 700 may also or instead include attenuating light at one or moreother wavelengths for any of a variety of purposes such as filtering orshaping a broadband light source, or attenuating within the medium inorder to permit additional measurements at other wavelengths that may beused to improve overall accuracy by providing additional thicknessmeasurements at a pixel location.

As shown in step 708, the method 700 may include determining a thicknessof the medium in the direction of the location based upon a function ofthe intensity of the first wavelength and the intensity of the secondwavelength, such as by calculating a ratio of the intensity of the firstwavelength to the intensity of the second wavelength and using thisrelationship to determine thickness. A more detailed analyticaldevelopment is now provided for thickness calculations in this context.

In an absorption-based method as described herein, two intensity bandscentered on wavelengths λ₁ and λ₂ may be selected where a medium'sabsorptivity coefficients ε_(λ1) and ε_(λ2) are different so that oneband is preferentially absorbed over the other (or alternatively stated,a medium may be selected with differential absorptivity at desiredwavelengths). The illumination source may contain the wavelengths λ₁ andλ₂, and the properties of the surface may be such that these two bandsare easily reflected back towards the sensor. Provided the surface has aknown, uniform color, or an otherwise known color pattern, the ratio ofintensities will vary predictably with thickness of the medium.

The geometry of the sensor and the illumination source need to beconsidered when calculating three-dimensional geometry in this contextbecause the wavelengths are absorbed as soon as the illumination sourcerays begin traveling through an absorbing medium. The simplest caseinvolves a coaxial imaging optical train and illumination source. Here,the absorption distance traveled is simply equal to twice the distanceof the sensor to the surface (or the medium boundary to the targetsurface), so that [Eq. 3] above becomes:

$\begin{matrix}{{I_{Ratio}(d)} = {\frac{\overset{\_}{I_{\lambda \; 1}}(d)}{\overset{\_}{I_{\lambda \; 2}}(d)} = {\frac{R_{1}}{R_{2}}^{\lbrack{{({ɛ_{\lambda \; 2} - ɛ_{\lambda \; 1}})}{C \cdot 2}\; d}\rbrack}}}} & \left\lbrack {{Eq}.\mspace{14mu} 12} \right\rbrack\end{matrix}$

Here, R₁ and R₂ are the reflectivities of the surface at wavelengths λ₁and λ₂, respectively. Because the intensity ratio decreasesexponentially as the distance through a medium increases, thisrelationship permits a calculation of thickness through the medium. Itwill be appreciated that in practice, actual measurements may beobtained and fit to this relationship using any suitable techniques inorder to provide calibrated thickness measurements from a workingsystem.

As shown in step 710, the method 700 may include reconstructing athree-dimensional image of the target surface. This may include, forexample, constructing a three-dimensional image of the region ofinterest with a two-dimensional array of thickness measurements (such asfrom a two-dimensional array of sensor measurements). This may furtherinclude constructing a three-dimensional image of the target surfacefrom a plurality of three-dimensional images of a plurality of regionsof interest, such as by registering or otherwise combining multiplethree-dimensional images.

It will be appreciated that the method 700 described above is set forthby way of example and not of limitation. Numerous variations, additions,omissions, and other modifications will be apparent to one of ordinaryskill in the art. In addition, the order or presentation of these stepsin the description and drawings is not intended to require this order ofperforming the recited steps unless a particular order is expresslyrequired or otherwise clear from the context. Thus, for example, asystem may measure intensity through a medium at three or more differentwavelengths in order to improve accuracy. As another example, thethree-dimensional reconstruction may include locating one or moreboundary surfaces of the medium using any number of fiducials within animaging chamber that holds the medium. As another example, the color orcolor pattern of the target surface may be predetermined by capturing acolor image of the target surface without an intervening medium thatselectively absorbs particular wavelengths. This baseline image mayprovide the predetermined color pattern needed for subsequent thicknesscalculations once a selectively-absorping medium is introduced betweenthe target surface and a sensor. The color image may, for example, becaptured from the same sensor(s) used to capture intensity data forthickness calculations, or from a separate color camera or the like. Allsuch modifications are intended to fall within the scope of thisdisclosure, which should be interpreted in a non-limiting sense.

FIG. 8 illustrates a computer-implemented method for three-dimensionalimaging using the technique described above. The method 800 may beimplemented, for example, as a computer program product embodied in acomputer-readable medium that when executing on one or more computingdevices performs the recited steps.

As shown in step 802, the method 800 may begin by characterizing a colorover a region of interest on a target surface to provide a predeterminedcolor for the region of interest. In order to perform thicknesscalculations as described in this embodiment, calculations exploit aknown color of the target surface (or more specifically, a knownreflectance at two or more specific wavelengths, although these twosomewhat different notions are treated as the same for the purposes ofthis description). Where the target surface has a known, uniform color,the predetermined color may be characterized in computer memory as oneor more scalar values that describe the color for the entire targetsurface (e.g., with a specific wavelength or RGB components of ameasured color), or that describe a reflectance o the surface at two ormore wavelengths where measurements are taken. Where a variable patternor the like is used, the predetermined color may be stored as an arraythat characterizes the spatial distribution of the color pattern on thetarget surface.

As shown in step 804, the method 800 may further include characterizinga first attenuation coefficient at a first wavelength and a secondattenuation coefficient at a second wavelength of a medium distributedbetween the target surface and a sensor. These values are used toevaluate the (expected) attenuation of light reflected from the targetsurface toward the sensor so that thickness can be calculated. Ingeneral, the attenuation coefficients may be assumed based upon themedium and any substances mixed in or otherwise distributed throughoutthe medium, or the attenuation coefficients may be measured using anysuitable techniques, such as in a calibration process or the like.

As shown in step 806, measurements may be received from the sensor,which may be any of the photosensors, pixel arrays, or other sensorsdescribed above that capture intensity in a direction of a location inthe region of interest. The measurements of an intensity at the firstwavelength and an intensity at the second wavelength may be provided assignals to a processor (or memory associated with a processor) for usein subsequent calculations.

As shown in step 808, the method 800 may include calculating a thicknessof the medium in the direction of the location based upon a function ofthe intensity of the first wavelength and the intensity of the secondwavelength. Suitable calculations are described above.

As shown in step 810, and as described more generally above, athree-dimensional reconstruction of the target surface may be obtained.In this reconstruction process, thickness measurements may be convertedinto a three-dimensional image of the target surface using, e.g., acombination of thickness measurements and associated directionalityalong with information about the geometry of the medium through whichthickness measurements are captured. Individual three-dimensional imagesmay also be aggregated into a composite three-dimensional image usingany suitable registration techniques.

It will be appreciated that the method 800 described above is set forthby way of example and not of limitation. Numerous variations, additions,omissions, and other modifications will be apparent to one of ordinaryskill in the art. In addition, the order or presentation of these stepsin the description and drawings is not intended to require this order ofperforming the recited steps unless a particular order is expresslyrequired or otherwise clear from the context. Thus, for example,characterizing a color of a target surface may include imaging thetarget surface with spectroscopic hardware that provides sufficientinformation on surface characteristics (without an interveningattenuating medium) to permit attenuation-based thickness measurements.In addition, the characterization of color, as well as attenuationcoefficients, may be performed before, during, or after the capture ofwavelength-specific intensity information. All such modifications areintended to fall within the scope of this disclosure, which should beinterpreted in a non-limiting sense.

FIG. 9 shows a method for using a single camera to measure thickness. Itwill be appreciated that the method 900 described with reference to FIG.9 may be embodied in a camera and processor coupled together andoperating as described, or the method 900 may be embodied in a computerprogram product including computer-executable code that when executingon one or more computing devices performs the recited steps.

As shown in step 902, the method 900 may begin with receiving a colorimage from a camera. The camera may, for example be anycommercially-available color camera that provides a two-dimensionalimage containing intensity measurements at, e.g., a red wavelength, agreen wavelength, and a blue wavelength. The camera may instead be acommercially-available color camera that provides a two-dimensionalimage containing intensity measurements at a cyan wavelength, a magentawavelength, and a yellow wavelength. It will be understood that eachsuch intensity measurement may, as a practical matter, represent anintensity across a range of wavelengths detected by the correspondingsensors, which may be relatively broad or narrow band measurements aboutthe respective red, green, and blue center frequencies according to thefilters, sensor sensitivity, and other hardware and processingcharacteristics of the camera. The two-dimensional image may take anynumber of forms, such as three arrays of pixel values for each of thered, green, and blue images.

As shown in step 904, the method 900 may include processing the colorimage to determine, for each one of a plurality of pixels of the camera,an intensity at a first wavelength and an intensity at a secondwavelength. Where the camera provides direct measurement at thewavelengths of interest, such as through a corresponding use of filters,these values may be used directly in subsequent thickness calculations.Where the camera instead provides RGB or CMY data, the wavelengths ofinterest may be inferred from the discrete color values contained in theimage.

As shown in step 906, the method 900 may include calculating a thicknessof a medium in a direction from the camera corresponding to each one ofthe plurality of pixels based upon the intensity at the first wavelengthand the intensity at the second wavelength, along with a knowncoefficient of attenuation of the medium for each of the firstwavelength and the second wavelength. More generally, any of thetechniques described above may be employed with a conventional colorcamera and suitable corresponding processing to capture thicknessmeasurements as described herein.

As shown in step 908, the method 900 may include providing athree-dimensional reconstruction of a target surface, such as using anyof the techniques described above. Step 908 may be performed by the sameprocessor that provides thickness calculations, or the thickness datamay be transferred to another process, processor, or machine that takesthickness data along with other geometric information (such as boundaryinformation for a medium) and reconstructs a three-dimensional image ofa target surface. In one embodiment, thickness calculations may beusefully integrated into a single device that contains the camera andthe processor, and that provides as an output an array of thicknesscalculations for use, e.g., in a desktop computer that performssubsequent three-dimensional reconstruction.

It will be appreciated that the method 900 described above is set forthby way of example and not of limitation. Numerous variations, additions,omissions, and other modifications will be apparent to one of ordinaryskill in the art. In addition, the order or presentation of these stepsin the description and drawings is not intended to require this order ofperforming the recited steps unless a particular order is expresslyrequired or otherwise clear from the context. All such modifications areintended to fall within the scope of this disclosure, which should beinterpreted in a non-limiting sense.

In another aspect, a system described herein may include an imagingmeans such as a camera or any similar sensor or collection of sensors asdescribed above for capturing a color image, along with a processingmeans including any of the processors or the like described herein thathas been programmed to perform the data processing steps above.

FIG. 10 illustrates an adaptation of the techniques described herein toimaging of an interior space such as a human ear canal. As shown in FIG.10, a system 1000 may include an inflatable membrane 1002 formed aboutan interior space 1004 with an interior surface 1006 and an exteriorsurface 1008, a seal 1010 having a first port 1012 and a second port1014, a supply 1016 of a medium 1018, a pump 1020, a light source 1022,a sensor 1024, and a computer 1025 with a processor 1026 and otherhardware 1028. It will be understood that, while the system 1000 may beused with any of the inventive imaging techniques described herein, thesystem 1000 may also or instead be adapted for use in known filmthickness measurement techniques such as ERLIF or any other similartechnology.

In general operation, the supply 1016 delivers the medium 1018 into theinterior space 1004 of the inflatable membrane 1002 under pressure sothat the inflatable membrane 1002 expands to fill an interiormeasurement volume (not shown). When the inflatable membrane 1002 isinflated so that it is in contact with and takes the shape of someportion of the interior measurement volume, the light source 1022 mayilluminate the interior surface 1006 of the inflatable membrane 1002,and the sensor 1024 may capture intensity measurements at two or morewavelengths using any of the techniques generally described above. Theresulting measurements may be received by the processor 1026 which maydetermine a thickness of the medium 1018 within the interior space 1004at one or more locations on the interior surface 1006 of the inflatablemembrane 1002, and these thickness measurements may be further processedto obtain a three-dimensional image of a portion of the interior surface1006.

The inflatable membrane 1002 may be a balloon or the like formed aboutan interior space 1004. In general, the inflatable membrane 1002 may bean elastic membrane formed of any rubber, elastic, or other materialthat can be stretch to expand when filled with a pressurized gas orother material. In embodiments, the inflatable membrane 1002 may also,or instead, be any expandable membrane, elastic or inelastic, that canbe pressurized or filled with material to increase an interior (and/orexterior) volume. Thus for example the inflatable membrane 1002 may beany of the membranes described above, or an inelastic membrane such asan expandable membrane formed from a number of non-porous, inelasticpanels such as MYLAR films or the like. This approach permits theinflated shape of the inflatable membrane 1002 to be matched to ananticipated cavity shape or size. In another aspect, the inflatablemembrane 1002 may have a substantially spherical or ovoid shape and befabricated of a material that permits the inflatable membrane 1002 tostretch and expand to fill a cavity. It will be readily appreciated thatdifferent sized balloons and other inflatable membranes may be employedin different cavities.

The inflatable membrane 1002 may be non-porous or otherwise capable ofretaining a pressurized gas or other material in an interior thereof sothat it can be inflated within an interior volume and, under pressure,take the form of the interior volume. In one aspect, the inflatablemembrane 1002 may be sufficiently flexible and elastic to closely followany contours of the interior volume as it inflates therein, andsufficiently thin that a measurement of the interior surface 1006 can beused to accurately infer a shape of the exterior surface 1008 when theinflatable membrane 1002 is inflated to contact the wall of such aninterior volume. More generally, any membrane capable of retaining amaterial within its interior space and capable of expanding to fill aninterior volume in a manner that closely follows the surface contoursthereof may be employed as the inflatable membrane 1002.

It will be appreciated that many variations are possible, and that anysurface of the inflatable membrane 1002 may be used for imaging. Forexample, the inflatable membrane 1002 may be fabricated from atransparent material, and the exterior surface 1008 may be coated with afluorescent or luminescent layer. In such embodiments, athree-dimensional reconstruction may account for the thickness of theinflatable membrane 1002 when reconstructing a target surface. Inanother aspect, a surface such as the interior surface 1006 may have apredetermined color such as a known, uniform color or a predeterminedcolor distribution to permit the use of certain imaging techniquesdescribed above. In another embodiment, the cavity that is to be imagedmay itself have a known color, or have a fluorescent or luminescentcoating applied thereto. Such a cavity may be imaged with an inflatablemembrane 1002 that is transparent and contains one of the imaging mediadescribed above, with suitable adjustments to account for the thicknessof the inflatable membrane 1002 between the medium and the surface ofthe cavity.

A seal 1010 may be used to isolate the interior space 1004 from anambient environment such as air at atmospheric pressure. The seal 1010may include any number of ports such as a first port 1012 and a secondport 1014 for accessing the interior space 1004. In embodiments, theseal 1010 may include an o-ring or the like, allowing for omission ofthe sleeve 1015. In such embodiments, a tight fit between the o-ring andthe optics, electronics and so forth that are inserted through it canretain the pressurized gas (or liquid medium, or the like) within theinterior space 1004.

The first port 1012 may, for example, be a fluid port having an open endwithin the interior space 1004 and may serve as a supply port to delivera medium such as a gas or any of the other media described above intothe interior space 1004 under pressure so that the inflatable membrane1002 can be inflated with a medium that is used to facilitate thicknessmeasurements. The first port 1012 may include a valve 1013 or the liketo control delivery of the medium 1018 into the interior space 1004.

The second port 1014 may serve as an access port for optics, lightsources, and the like that might be inserted into the interior space1004 to capture data for thickness measurements. The second port 1014may be coupled to a sleeve 1015 that physically contains such hardwareas it is inserted into and removed from the interior space 1004. In oneaspect, the sleeve 1015 may be an elastic or extendable sleeve that iscoupled to the light source 1022 and/or sensor 1024 and permits thelight source 1022 and/or sensor 1024 to move about within the interiorspace 1004 of the inflatable membrane 1002 when inflated. In anotheraspect, the sleeve 1015 may be a transparent, rigid shell or the likedefining an access space 1017 within the inflatable membrane 1002 andphysically isolated from the remainder of the interior space 1004 thatis pressurized and medium-filled. In this manner an optical supply suchas a fiber optic bundle or the like, lenses, filters, or other optics,sensors, light sources, electronics (e.g., for operation of the sensorsand/or light sources), wires or other electrical coupling for a powersupply, and so forth can be freely inserted into and removed from theinterior space 1004 (or more precisely, the access space 1017 within theinterior space 1004) while preserving the seal 1010 on the inflatablemembrane 1002 and retaining, e.g., a pressurized gas or the like. Inanother aspect, the sleeve 1015 (or a window, viewport, or the likewithin the sleeve 1015) may be index-matched to the medium so that ithas substantially the same index of refraction as the medium. This mayprovide a substantially undistorted optical path into the medium-filledinterior space 1004.

The supply 1016 may be any reservoir, tank, or other container thatholds a supply of a medium 1018, which may be any of the media describedabove such as a gas, liquid, gel, or the like. In general, the supply1016 may be any supply capable of pressurized delivery of the medium1018. In embodiments, the supply 1016 may include a pump 1020 or otherdevice to deliver the medium 1018 through the first port 1012 and intothe interior space 1004 under pressure, or similarly to withdraw themedium 1018 from the interior space 1004. The pump 1020 may be anyelectromechanical device capable of pressurized delivery of the medium1018 including a rotary-type pump, a peristaltic pump, areciprocating-type pump, a centrifugal pump, an eductor-jet pump, ahydraulic ram pump, and so forth. The supply 1016 may include a usercontrol, which may be remotely activated by the computer 1025 orprovided as a switch, knob, dial, or the like on the supply 1016 thatelectrically controls the pump 1020. In embodiments, the supply 1016 mayinclude a plunger, lever, knob or similar device for manual applicationof pressure to the medium 1018, or for other mechanical delivery (alsounder pressure) of the medium 1018, any of which may serve as the pump1020 as that term is used herein. More generally, the supply 1016 may becoupled to the interior space 1004 in any manner that permits selectivedelivery of the medium 1018 into the interior space 1004. The pump 1020may, for example, deliver the medium 1018 with a controlled pressure, ormay deliver a controlled volume of the medium 1018, or may operateaccording to any other suitable criteria. In another aspect, the supply1016 may be a pressurized elastic container that contracts to deliverthe medium 1018.

The light source 1022 may include any of the light sources describedabove. In one aspect where the inflatable membrane 1002 is renderedluminescent, the light source 1022 in the access space 1017 may beomitted. In one aspect, the light source 1022 may be shaped and sizedfor insertion into the access space 1017 (through the second port 1014)or otherwise positioned within the interior space 1004. In anotheraspect, the light source 1022 may be, e.g., a luminescent layerdistributed on the interior surface 1006 or directly on a target surfaceof an interior cavity, or the light source 1022 may be positioned on theseal 1010 or in any other location to achieve illumination of a locationon a target surface of the inflatable membrane 1002 suitable for themeasurement techniques described herein.

The sensor 1024 may include any of the sensors described above. Thesensor 1024 may be shaped and sized for insertion into the access space1017 through the second port 1014, or otherwise inserted into theinterior space 1004 of the inflatable membrane 1002. In one aspect, afiberscope or boroscope may be used (either within the access space 1017or with the sleeve 1015 attached thereto), optionally with any suitablelens such as a prism or mirrored surface with a conical, parabolic,angled, or other tip (which may also be index-matched to the medium1018). It will be understood that in such embodiments, the sensor 1024may have a field of view that captures measurements from a cylindricalcross-section of the interior space. This may present a significantlydifferent geometry and different directionality for intensitymeasurements as compared to a conventional camera and lens, and suitableadjustments to groups of spatial measurements and any subsequentthree-dimensional reconstruction may be appropriate.

In some embodiments, a transparent index-matched tip of known dimensionscan be added to a fiberscope in order to improve the optical paththrough the medium 1018. This may allow the use of higher-absorptivitymedia, thus increasing the depth resolution of the system at largerdistances from the tip. In other words, such a tip can shift theexponential curve that relates ratio to depth so that the relationshippermits greater depth measurements.

The computer 1025 may include a processor 1026 such as any of theprocessors or other computing devices described above. The computer 1025may also include other hardware 1028 such as input/output interfaces,memory, and so forth. The other hardware 1028 may in general include anyhardware that operatively couples to the sensor 1024, the light source1022, and the supply 1016. In one aspect, the other hardware 1028 mayinclude an electronic imaging device such as optical transducers or apixel array with inputs coupled by fiber optics to the sensor 1024. Inanother aspect, the other hardware 1028 may include an illuminationsource coupled by fiber optics to the light source 1022. In anotheraspect, the sensor 1024 and/or light source 1022 may be electronicdevices electronically coupled to the computer 1025 with wires or thelike. In another aspect, the light source 1022 and sensor 1024 may beself-powered and wirelessly coupled to the computer 1025 for control andoperation of same. The computer 1025 may also be coupled to the supply1016, and may control operation of the pump 1020 to deliver the medium1018 to (and/or remove the medium 1018 from) the interior space 1004 ofthe inflatable membrane 1002.

The inflatable membrane 1002 may include a cap 1030, which may be asoft, pliable cap formed of a soft foam or similar substance. The cap1030 may protect an insertion site such as a human ear canal duringinsertion of the inflatable membrane 1002, such as where the sleeve 1015is formed of a hard material that might otherwise cause discomfort orphysical damage.

It will be understood that the system 1000 may also include any of avariety of other status sensors, spatial sensors, and so forth which maycooperate with the computer 1025 to control operation of the system 1000and monitor status thereof.

In general, the system 1000 may be adapted to use with any of theimaging techniques described above. For example, where the imagingtechnique uses a fluorescent layer applied to a target surface, theinflatable membrane 1002 may be adapted so that the interior surface1006, the exterior surface 1008, or the inflatable membrane 1002includes a fluorescent material (such as and without limitationcoumarin-153) or the like. Thus in one aspect there is disclosed hereinan inflatable membrane that includes a fluorescent interior surface,which membrane may be employed to capture three-dimensional images of aninterior volume in which the membrane is inflated. Similarly, apredetermined or known color may be employed on the interior surface asgenerally described above (although additional refinements to theprocessing might be required where, for example, the color of theballoon changes as it expands), or the predetermined color may be on orapplied to a target surface in a cavity.

The system 1000 for interior measurement may be more specificallyadapted to a particular imaging context. For example, the inflatablemembrane 1002 may be shaped and sized for insertion into (and inflationwithin) a human ear canal, or more specifically, may have a compressed(e.g., non-inflated) shape that is shaped and sized for insertion into ahuman ear so that the inflatable membrane 1002 may be inserted into theear canal, inflated, and then used to capture a three-dimensional imageof the ear canal. More generally, the system 1000 may be usefullyemployed to image biological cavities such as a bladder, stomach, earcanal, and so forth, or to image machine parts such as piston chambers,tanks, and other containers.

In one aspect there is disclosed herein a system including an inflatingmeans, an illuminating means, a sensor means, and a processor means. Theinflating means may be the supply 1016 or any other means for inflatingthe inflatable membrane with a medium that absorbs a first wavelength oflight more than a second wavelength of light. The illuminating means mayinclude the light source 1022 described above or any other meansdescribed herein for illuminating or otherwise exciting a surface of theinflatable membrane. The sensor means may include the sensor 1024 or anyother means described herein for measuring an intensity of the firstwavelength and an intensity of the second wavelength at a location onthe surface when illuminated by the illuminating means. The processormeans may include the processor or any other means described herein thatis programmed to calculate a thickness of the medium in a direction ofthe location based upon a function of the intensity of the firstwavelength and the intensity of the second wavelength.

In embodiments, the system 1000 may be adapted for the measurement ofmore general targets, not just for interior measurements or ear canals.In such embodiments, the inflatable membrane 1002 may be moved intocontact with a remote object so as to conform to a surface of thatobject. Here, the inflatable membrane 1002 may contain or be inflated tocontain the medium. For example, the inflatable membrane 1002 mayinclude a floppy or otherwise highly-deformable bag containing themedium. Such an inflatable membrane 1002 may conform to an object sothat a three-dimensional image can be obtained. This may for example beusefully employed for quality control or parts inspection, such as withturbine blades or other dimensional-sensitive parts. This approachpermits three-dimensional measurements without modifications of thetarget object, and without exposing the target object to the medium. Avariety of other uses will be readily appreciated, and are intended tofall within the scope of the present disclosure.

In some embodiments, the system 1000 may be adapted so that theinflatable membrane 1002 includes more than one chamber. Each of thesechambers may be operatively coupled to its own supply 1016, each ofwhich contains a medium having properties that are adapted based uponthe expected dimensions of the part of a canal into which the inflatablemembrane 1002 will ultimately be disposed. For example and withoutlimitation, one may expect an external portion of an ear canal to bewider than an internal portion of the same ear canal. Therefore, inapplications involving an ear canal, a first chamber corresponding to anexternal part of the ear canal might be filled with less absorptiveoptical media than a second chamber corresponding to an internal part ofthe ear canal. Such an adaptation allows the same source illumination totravel greater distances through the first chamber (where the distancesare expected to be longer) than through the second chamber (where thedistances are expected to be shorter). In embodiments, opticalcharacteristics of the media may be tuned with dye composition and/ordye concentration, as well as with different fluorescent coatings foreach chamber. The sleeve 1015 may pass into or through each of thechambers and preferably is index-matched to each of the media, or aseparate sleeve may be provided for each chamber.

FIG. 11 is a flow chart of a method for obtaining a three-dimensionalimage of an interior space. In general, the method 1100 may includepositioning an inflatable membrane such as any of the inflatablemembranes described above within a cavity and inflating the membranewith a medium such as any of the media described above. With suitableillumination sources and image capture hardware, thickness measurementsmay then be taken for use in a three-dimensional reconstruction ofinterior walls of the cavity. The method 1100 may be implemented, forexample, using the system described above.

As shown in step 1102, the method may begin with positioning aninflatable membrane in a cavity. It will be appreciated that this stepmay be adapted to an array of interior cavities. For example, where abiological cavity such as a stomach or bladder is being imaged, themembrane may be compressed into a shape and size that can be insertedthrough a natural opening (such as the throat) or through the bore of asurgical tool such as an endoscope or the like. Thus, the cavity may bea human ear canal, a stomach, a bladder, or any other biological cavity,or more generally, any of the cavities described above. It will bereadily appreciated that the inflated and compressed sizes of thebladder and the desired resolution of a particular image may beconsidered in selecting a suitable material for the membrane, which mayrange from elastic materials to very thin, flexible, inelastic filmssuch as foils and various composites. For use in imaging a human earcanal, for example, the diameter of the insertion site is relativelylarge compared to the cavity being imaged, and a variety of elasticmaterials may be suitably employed.

It will also be understood that in various techniques that use amembrane, the material selected for the membrane may depend in part uponthe types of surfaces expected and the surface accuracy desired forimaging. This in some applications, detail may be important and verythin, very elastic materials may be preferably employed in order toimprove surface detail. In other applications, high inflation pressuremay be desired and suitably strong materials may be preferred regardlessof the fidelity with which detailed surface contours are captured. Ingeneral, a wide variety of suitable membranes are known and may beadapted to different imaging applications. All such variations areintended to fall within the scope of this disclosure.

As shown in step 1104, the method 1100 may include inflating theinflatable membrane with a medium that absorbs a first wavelength oflight more than a second wavelength of light. This may be, for example,any of the media described above. Inflation may be, for example with apump or other manual or automated delivery mechanism as generallydiscussed above. As the inflatable membrane inflates, it may take theform of the cavity in which it is expanding, and the medium within themembrane may facilitate thickness measurements that can be used toreconstruct a three-dimensional image of the interior of the cavity.

As shown in step 1106, the method 1100 may include illuminating asurface of the inflatable membrane. This may include, for example,activating a light source such as any of the light sources describedabove, or chemically or electrically activating a luminescent substancewithin the inflatable membrane (or disposed on a surface thereof). Itwill be appreciated that in various embodiments described above, theillumination may be directed at another surface, such as the wall of acavity that is being imaged (e.g., with a transparent membrane and afluorescent cavity wall). In such embodiments, the surface of theinflatable membrane would also be illuminated regardless of the positionof the illumination source, and all such variations are intended to fallwithin the scope of “illuminating” as that step is described here.

As shown in step 1108, the method 1100 may include measuring anintensity of the first wavelength and an intensity of the secondwavelength in a direction of a location on the surface when the surfaceis illuminated. This may include measuring wavelength intensities usingany of the sensors described above including, for example, using aconical-tipped fiberscope or the like to transmit optical signals overoptical fibers to an electronic imaging device outside the membrane. Inone aspect, this may include capturing measurements in a cylindricalfield of view of a fiberscope.

As shown in step 1110, the method 1100 may include calculating athickness of the medium in the direction of the location based upon afunction of the intensity of the first wavelength and the intensity ofthe second wavelength using, e.g., any of the techniques described aboveaccording to the nature of the surface, the medium, and the like. Step1110 may be performed by any suitable processor or other computingdevice or combination of computing devices.

As shown in step 1112, the method 1100 may include reconstructing athree-dimensional image of the surface based upon the thicknessmeasurements and available boundary information for the medium. So forexample where a clear plastic tube or other transparent, rigid sleeve isused for sensors and the like, the thickness measurements may beprojected from the physical interface of the sleeve with the medium.Step 1112 may be performed by any suitable processor or other computingdevice or combination of devices.

In some embodiments, the method 1100 includes an iteration in which theinflatable membrane inflates to a first pressure and a calculationdetermines a first thickness of the medium, as described above. Then theinflatable membrane inflates again, this time to a second pressure, anda calculation determines a second thickness of the medium, again asdescribed above. When the first measurement and the second measurementcorrespond to the same point of interest on an object, and when aplurality of such measurements are made for a plurality of points ofinterest on the object, the method 1100 can include a step of generatinga compliance map that shows relative firmnesses of the object at thepoints of interest, or the manner in which a cavity yields to pressure.For example, a point of interest that shows greater change in thickness(e.g., yields to greater pressure) between the first measurement and thesecond measurement has more “give” than a point of interest that showsless change in thickness between the measurements. Thus, step 1112 caninclude or consist of calculating the compliance map and the logicalflow of the method 1100 can include a loop from step 1110 back to step1104 for any number of measurements under different pressurization.

FIG. 12 shows a self-inflating bladder for use in interior measurements.In general, the self-inflating bladder 1200 may include a membrane 1202such as a collapsible membrane including many elements of the system1000 described above, with differences as noted below.

The membrane 1202 may be formed around an interior space 1004, andconstructed of a material that returns to an original shape in anabsence of external forces. For example, the membrane 1202 may be formedof a shape-memory alloy, a visco-elastic solid or foam, a photo-inducedshape-memory polymer, a shape-memory rubber, or any other film, frame,lattice, composite exterior and/or interior structure or combination ofstructures that return to an original shape. The membrane 1202 may beshaped and sized (in its expanded form) to be larger than a cavity thatis to be imaged in one or more dimensions so that the membrane 1202,when compressed into a compressed membrane, can be inserted into thecavity and then expand to contact the interior wall of the cavity. Moregenerally in operation, the membrane 1202 may be compressed with anapplication of force, and then released to expand to its original shape,such as to fill a cavity for imaging. In one aspect, the membrane 1202may be fabricated of a material that returns to an original shape underuser-controlled conditions such as an application of heat, moisture, anelectrical field and so forth. It will be understood that in suchembodiments, the membrane 1202 will tend to return to an original shapein the absence of physical external forces along with an application ofthe appropriate form of activation. All such variations are intended tofall within the scope of a membrane returning to an original shape inthe absence of external forces as that phrase is used herein.

It should also be understood that the compressed membrane need not havea reduced volume in order to be “compressed” as that term is usedherein. For example, where a generally elastic membrane is filled with aviscous substance, the membrane may be elongated with an application offorce so that it has greater length and less thickness. In thiscompressed state, the membrane may be inserted into a narrow passage(such as an ear canal) and the membrane may then expand to abut thewalls of the passage as it returns to its original, thicker shape. Thuswhile a variety of embodiments discussed herein involve displacement ofa medium into and out of a membrane, in other embodiments a collapsiblemembrane may be compressed by displacing the medium within the membranewithout any overall change in volume of the membrane. In suchembodiments, the membrane may be advantageously fabricated in a sealedform without any fluid port or the like for manipulating the mediumwithin the membrane.

The interior space 1004 may be coupled to a supply 1016 of a medium 1018(which may be any of the supplies and media described above) through thefirst port 1012, which in this case may be a fluid port, that couplesthe supply 1016 to the interior space 1004 and includes a flowrestrictor 1213 or the like that controls a rate at which the medium1018 passes between the supply 1016 and the interior space 1004. Thismay include, for example, a porous membrane, nozzle, narrowed fluidpassage, adjustable valve (for variable control of flow rate) or anyother substance or structure (or combination of these) to slow thepassage of the medium 1018 into the interior space 1004 when themembrane 1202 is expanding. In general, by restricting a flow of themedium 1018, the flow restrictor 1213 limits that rate at which themembrane 1202 expands in the absence of external forces. This usefullypermits the membrane 1202 to be compressed with an application of forceand then released, at which point the membrane 1202 will expand slowlyenough that it can be inserted into a cavity before it fully expands.

A sleeve 1015, which may be a shell such as any of the rigid shellsdescribed above, may be positioned within the interior space 1004 todefine an access space 1017 for insertion of a light source 1022, sensor1024 and the like to facilitate light intensity measurements. The sleeve1015 may be fabricated of a transparent material, or otherwise includeat least one transparent region for such measurements. The sleeve 1015may extend from a seal 1010 to the cap 1030, which may be a soft,pliable cap such as any of the caps described above. In one aspect, thesleeve 1015 may physically connect to the cap 1030 and the seal 1010,either directly or through additional structures, to form a solid orgenerally rigid structure that, along with the supply 1016 and the firstport 1012, can be used as an insertable imaging device. Where theself-inflating bladder 1200 is shaped and sized for use in, e.g., ahuman ear canal, the cap 1030 may be soft and/or pliable to protect theear canal during insertion of the device.

The cap 1030 may include a transparent window. During insertion of theself-inflating bladder 1200 (or any other device described herein forinterior imaging) into, e.g., an ear canal or other opening, afiberscope can be inserted into the access space 1017 so that it has anoptical view through the window and the sensor 1024 can capture an imagedown the length of the ear canal. With this view, a user may guide theself-inflating bladder 1200 (or other device) into the canal, alsoallowing the user to stop insertion before hitting, e.g., an eardrum orother obstruction or sensitive area. The self-inflating bladder 1220 (orother device) may include a supplemental illumination device toilluminate the canal during insertion, or the light source 1022 may beadapted to this purpose.

In one aspect a retainer 1216 may be provided that mechanically retainsthe collapsible membrane in a compressed shape. Thus in use, themembrane 1202 may be compressed to a size smaller than an interiordiameter of the retainer 1216, which may be for example a cylindricalsleeve or the like, and the retainer 1216 may be fitted over thecompressed shape to retain the membrane 1202. When a three-dimensionalimage is to be captured, the retainer 1216 may be removed and theself-inflating bladder 1200 may be inserted into a target cavity andpermitted to slowly expand into the shape of the target cavity, with therate of expansion determined by, e.g., the viscosity of the medium 1018,the flow restrictor 1213 positioned in the flow path, and the mechanicalforce applied by the membrane 1202 as it expands toward its fullyexpanded shape. It will be understood that the retainer 1216 mayusefully be formed of a rigid material (or combination of materials) orany other material suitable for retaining the membrane 1202 in acompressed state. The retainer 1216 may be a single structure shaped andsized to slide over the cap 1030 and off the membrane 1202, or theretainer 1216 may be formed of a multi-part assembly that can be, e.g.,snapped together and apart around the membrane 1202, or that hingeablyencloses the membrane 1202, or otherwise removably retains the membrane1202 in a compressed shape. The compressed shape may be shaped and/orsized for insertion into a human ear or any other cavity from whichthree-dimensional images are desired.

It will be understood that while FIG. 12 shows a simple, cylindricalshape for the membrane 1202 in its compressed state, any shape suitablefor a particular imaging application may similarly be used, and mayaccommodate either the shape and size of the insertion site or the shapeand size of the cavity to be imaged, or some combination of these. Forexample, the inner and outer portions of a human ear canal havesubstantially different interior diameters. Thus in one aspect, theself-inflating bladder 1200, and the membrane 1202 and retainer 1216 forsame, may have a tapered shape or a two-stage shape with a relativelylarge diameter on an outer section for imaging the outer ear canal and arelatively smaller diameter on an inner section for imaging more deeplyin the inner ear canal. Any number of similar adaptations may be madefor different imaging applications, all of which will be readilyappreciated by one of ordinary skill in the art.

FIG. 13 is a flow chart of a method for using a self-inflating bladdersuch as the self-inflating bladder 1200 described above to capturethree-dimensional images of an interior space, and more particular tocapture three-dimensional images of a human ear canal.

As shown in step 1302, the method 1300 may begin with providing acollapsible membrane that returns to an original shape absent externalforces, the collapsible membrane having an interior space. This may be,for example, any of the membranes described above. As noted above, amembrane that returns to an original shape absent external forces isintended to include any structure or combination of structures that tendto return to a shape, whether when constraining physical forces arereleased (e.g., a retainer as described above) or when some form ofactivation (light, heat, electricity, and so forth) is applied, or somecombination of these.

As shown in step 1304, the method 1300 may include compressing thecollapsible membrane into a shape and size for fitting into a human earcanal. This may, for example, include compressing the membrane into agenerally cylindrical shape sufficiently narrow to fit into the earcanal. In one aspect, a margin of time may be provided so that, when aretainer is removed and the membrane begins to expand (as describedabove), the membrane does not expand beyond the expected size of the earcanal for a period of time in order to permit handling and insertioninto the ear canal. This may be, for example, ten seconds, or any otherduration according to user preferences or handling constraints and thelike.

As shown in step 1306, the method 1300 may include retaining thecollapsible membrane in the shape and size with a retainer such as anyof the retainers described above. In one aspect, the collapsiblemembrane may be a disposable membrane with a disposable retainer. Inanother aspect, the collapsible membrane may be a reusable membrane, andthe retainer may be removable and replaceable to permit multipleredeployments of the collapsible membrane.

As shown in step 1308, the method 1300 may include coupling the interiorspace to a supply of a medium in a fluid form that absorbs a firstwavelength of light more than a second wavelength of light, wherein theinterior space is coupled to the medium through a port that restricts aflow of the medium into the interior space, such as the fluid port andflow restrictor described above. It will be understood that in variousembodiments this coupling may occur before or after the collapsiblemembrane is compressed and before or after the retainer is fitted to thecompressed membrane.

As shown in step 1310, the method 1300 may include removing the retainerfrom the collapsible membrane and inserting the collapsible membraneinto a human ear canal. At this point, the membrane may begin to expandand draw the medium into the interior space. As noted above, the rate atwhich this expansion occurs may depend on any of a number of factorssuch as the viscosity of the medium, the amount of flow restriction, thepressure created by the expanding membrane, and the pressurization (ifany) of the supply. These factors may generally be controlled duringdesign of the collapsible membrane, and the design may also permitmanual adjustment at the time of deployment such as by providing anadjustable valve for flow restriction.

As shown in step 1312, the method 1300 may include measurement andthree-dimensional reconstruction using any of the techniques describedabove.

It will be appreciated that the method 1300 described above is set forthby way of example and not of limitation. Numerous variations, additions,omissions, and other modifications will be apparent to one of ordinaryskill in the art. In addition, the order or presentation of these stepsin the description and drawings is not intended to require this order ofperforming the recited steps unless a particular order is expresslyrequired or otherwise clear from the context. Thus, for example a mediummay be coupled to the membrane before or after compression of themembrane. Where the medium is coupled before compression of themembrane, the supply may be used to compress the membrane using reversepressure (e.g., suction) to extract material from the interior space.Similarly, while an ear canal is specifically mentioned, the approachmay be adapted to any number of biological or other cavities. All suchmodifications are intended to fall within the scope of this disclosure,which should be interpreted in a non-limiting sense.

FIG. 14 illustrates an adaptation of the techniques described herein tocapture a three-dimensional image of an object such as human dentition.In an embodiment, a device 1400 for use in imaging dentition may includean imaging tray 1402 with an interior surface 1404 formed from a bottom1406 and one or more sidewalls 1408, and any number of fiducials 1410,along with a medium 1412 such as any of the media described above.Although not depicted, it will be understood that the device 1400 may beused with any suitable combination of the sensors, light sources,processors, and so forth described above. It will further be understoodthat, while the device 1400 may be used with any of the inventiveimaging techniques described herein, the device 1400 may also or insteadbe adapted for use in known film thickness measurement techniques suchas ERLIF or any other similar technology.

The imaging tray 1402 may be any container suitable for receiving animpression of an object. For dental applications, the imaging tray 1402may be shaped and sized for use as a dental bite tray. A variety of suchcontainers are known in the dental art including numerous disposableand/or reusable bite trays, impression trays, fluoride trays and thelike, any of which may be adapted for use with the techniques describedherein. In addition, while a full-arch dental tray is shown, it will beunderstood that the tray may instead cover any sub-portion of an archsuch as a quadrant or a row of teeth. In other embodiments, the bitetray may capture an upper and lower arch concurrently, which mayadvantageously capture bite registration information relating to thealignment of an upper and lower arch. It will be appreciated that whilea dental bite tray is depicted, the imaging tray 1402 may more generallyhave any shape and size suitable for an object that is to be imaged. Inaddition, the imaging tray 1402 may be adapted to any of the variousimaging techniques described above. This may include, for example,fabricating the imaging tray 1402 from a transparent material so thatthickness measurements can be taken through the imaging tray 1402, orfabricating the imaging tray 1402 from a fluorescent or otherluminescent material so that the imaging tray 1402 can serve as a lightsource as described above. This may include fabricating the imaging tray1402 from a material with a known color or a known color distributionthat can be used in attenuation measurements as described above. Thismay also, or instead, include applying a layer to the interior surface1404, such as a fluorescent, luminescent, or known color layer.

The interior surface 1404 may have known dimensions that can be used incombination with thickness measurements to geometrically reconstruct athree-dimensional image of an object impressed into the medium 1412. Inone embodiment, the known dimensions may accommodate a dental impressionin the medium 1412. More generally, geometric or spatial informationabout the interior surface 1404 provides boundary information for themedium 1412 within the imaging tray 1402 so that thickness measurementsof the medium 1412 can be converted into spatial measurements of animpression in a common coordinate system, thus permitting athree-dimensional reconstruction. It will thus be appreciated that,while the imaging tray 1402 is depicted as having an interior surface1404 formed of two sidewalls 1408 and a bottom 1406, the interiorsurface 1404 may more generally include any rectilinear, curvilinear orother surface(s) suitable for a particular object being imaged, providedthat the shape of the interior surface 1404 is known in areas whereboundary positions are needed for a three-dimensional reconstruction.

The bottom 1406 and sidewalls 1408 retain the medium 1412 within theimaging tray 1402 and provide known physical boundaries for one or moresurfaces of the medium 1412 so that thickness measurements can beconverted into a three-dimensional image. It will be appreciated thatthe sidewalls 1408 may be open as depicted, provided the medium 1412 issufficiently viscous that it will remain wholly or partially within theimaging tray 1402 during handling and/or impressioning. Where forexample the medium 1412 is a non-viscous liquid, the sidewalls 1408 mayusefully be joined together to form a complete perimeter sidewall thatretains the liquid within the imaging tray 1402. In another aspect, oneor more of the bottom 1406 and sidewalls 1408 may be transparent,depending for example on the direction from which thickness measurementsare expected to be taken.

Any number of fiducials 1410 may optionally be included on or within theimaging tray 1402. The fiducials may be at known locations and/or have aknown shape. Each fiducial 1410 may have one or more uniquelyidentifying characteristics so that it can be identified in an image orother data obtained from measurements of the imaging tray 1402.Fiducials may in general serve as useful landmarks in athree-dimensional reconstruction by facilitating global registration ofa number of independent three-dimensional measurements and/or images.The fiducials 1410 may, for example, provide visual landmarks to animaging system that can be correlated to three-dimensional locations onthe imaging tray 1402 or otherwise encode spatial information. Moregenerally, the types and uses of fiducials in three-dimensionalregistration will be readily appreciated by those of ordinary skill inthe art, and all such fiducials that might be adapted to use with thethree-dimensional imaging techniques described herein are intended tofall within the scope of this disclosure. Similarly, random or regularpatterns or other surface treatments can be employed to assist inregistration, and may be adapted for use with the imaging tray 1402 andother devices and measurement techniques described herein.

The medium 1412 may be disposed within the interior surface 1404 and maygenerally include any of the media described above. In an embodiment,the medium 1040 may be capable of yielding to form an impression of anobject inserted into the imaging tray and may, for example, absorb afirst wavelength of light more than a second wavelength of light. Themedium 1412 may include a single fluorescent dye or a plurality offluorescent dyes. The medium 1412 may use any number of carriers.

For example, the medium 1412 may include a gel, liquid, or othersubstance capable of accurately retaining, or being cured to accuratelyretain, an impression therein. Any type of curable material (withsuitable optical properties) may be used as the carrier, includingmaterials that are heat-cured, pressure-cured, time-cured, light-cured,chemically cured, or the like, as well as any combination of these. Themedium 1412 may be cured while an object is impressed therein, such aswhile a patient is biting into a dental bite tray, or the medium 1412may be cured after the object is withdrawn. In the latter case, themedium 1412 is preferably sufficiently viscous to retain a usefulimpression of the object until the medium 1412 can be cured. In otherembodiments, the medium 1412 may not be curable, but may be sufficientlyviscous or plastic to retain an accurate impression after an object isremoved, either permanently, semi-permanently, or at least long enoughto obtain light intensity measurements for thickness calculations. Inother embodiments, the medium 1412 and imaging tray 1402 may be imagedwhile the object is embedded in the medium. Where the object fitsentirely into the imaging tray 1402, the imaging tray 1402 may be asimple desktop tray filled with liquid or the like. Where the object isphysically coupled to a larger object (such as human dentition), theimaging tray 1402 may be transparent so that measurements for thicknesscalculations can be obtained through the bottom 1406 or sidewall(s)1408.

FIG. 15 is a flow chart of a method for capturing a three-dimensionalimage of an object such as human dentition using the techniquesdescribed herein. The method 1500 may be used, for example, with theimaging tray 1402 and medium 1412 described above.

As shown in step 1502, the method 1500 may begin with disposing a mediumwithin an imaging tray having an interior surface of known dimensions,the medium capable of yielding to form an impression of an objectinserted into the imaging tray, and the medium absorbing a firstwavelength of light more than a second wavelength of light. In general,this may include any of the imaging trays and mediums described above.In order to dispose the medium within the imaging tray, the medium maybe poured, injected, spread, or otherwise distributed into the interiorspace using any suitable tools and/or techniques for the viscosity andother physical properties of the medium. In a prepackaged embodiment,the medium may be disposed within the imaging tray during fabrication,and packaged for shipment in a ready to use form. In another embodiment,the medium may be manually disposed within the imaging tray prior touse, such as from a tube or other container of the medium. In eithercase, the imaging tray may be reusable or disposable.

As shown in step 1504, the method 1500 may include inserting an objectinto the imaging tray. This may include placing an object into theimaging tray (such as where the medium is a liquid), or applying a forceto insert the object into the medium within the imaging tray. Forexample, where the imaging tray is a dental bite tray, this may includeinserting human dentition into the dental bite tray, such as by having auser apply force by biting into the medium with the teeth and otherdentition that are the object of the impression. However inserted, theobject may in general displace the medium and form an impression of theobject within the medium.

As shown in step 1506, the method 1500 may include illuminating theinterior surface of the imaging tray. This may include any of theillumination techniques described above.

As shown in step 1508, the method 1500 may include capturing an image ofthe interior surface at the first wavelength and the second wavelength.This may in general include any of the imaging techniques describedabove. It will be understood that capturing an image in this context isintended to refer to the direction of the surface rather than thesurface itself. Thus for example where a transparent imaging tray isused, the image captured may be an intensity of light from a mediumbehind the interior surface rather than the interior surface itself.Thus in many embodiments the image may relate to the direction in whichlight intensity is measured rather than an actual location from whichlight is reflected.

Capturing an image of the interior surface may also, or instead, includecapturing a reference image of a plurality of fiducials provided withinthe imaging tray. These fiducials may be used to determine athree-dimensional position and orientation of an imaging tray using anyof a variety of known techniques. This may include processing of thesame image used to calculate thicknesses (e.g., an image of the interiorsurface at the first wavelength and the second wavelength), such as bylocating and interpreting the fiducials in such images, or this mayinclude capturing a supplemental image with the same camera or sensor(s)for processing of the fiducials. In another aspect, a supplementalcamera or other imaging device may be provided in order to capture areference image of the fiducials. In such embodiments, the supplementalcamera should have a known spatial relationship to the camera or sensorsused for thickness measurements.

As shown in step 1510, the method 1500 may include processing the imageto determine a thickness of the medium in a direction of the interiorsurface. This may include any of the processing techniques describedabove based upon a ratio of intensities of two different wavelengths oflight, or any other similar technique or approach. This may includecapturing a plurality of thickness measurements for a plurality ofdirections toward the interior surface, such as from a two-dimensionalarray of intensity measurements captured by a camera or the like.

As shown in step 1512, the method 1500 may include obtaining athree-dimensional reconstruction of the object from the thicknessmeasurement(s). This may include, for example, applying a number ofthickness measurements, in view of the known dimensions of the interiorsurface, to determine a three-dimensional shape of the object, or theboundaries of an impression of the object in the medium. It will beunderstood that for a variety of reasons there may be subtle orsubstantial deviations between the actual object shape and the actualimpression of the object. Either or both of these (conceptually)mirror-imaged surfaces are intended to fall within the scope of thethree-dimensional shape of the object as that phrase is used herein.

It will be appreciated that the method 1500 described above is set forthby way of example and not of limitation. Numerous variations, additions,omissions, and other modifications will be apparent to one of ordinaryskill in the art. In addition, the order or presentation of these stepsin the description and drawings is not intended to require this order ofperforming the recited steps unless a particular order is expresslyrequired or otherwise clear from the context. Thus, for example theobject may be inserted into an imaging tray before the medium isdisposed therein. Or various types of fiducials may be used to relatethickness measurements to positions within the imaging tray. Similarly,while human dentition is specifically mentioned, the approach may beadapted to a wide variety of biological or other subject matter, and allsuch variations are intended to fall within the scope of the presentdisclosure.

It will be appreciated that any of the above systems, devices, methods,processes, and the like may be realized in hardware, software, or anycombination of these suitable for the control, data acquisition, anddata processing described herein. This includes realization in one ormore microprocessors, microcontrollers, embedded microcontrollers,programmable digital signal processors or other programmable devices,along with internal and/or external memory. This may also, or instead,include one or more application specific integrated circuits,programmable gate arrays, programmable array logic components, or anyother device or devices that may be configured to process electronicsignals. It will further be appreciated that a realization of theprocesses or devices described above may include computer-executablecode created using a structured programming language such as C, anobject oriented programming language such as C++, or any otherhigh-level or low-level programming language (including assemblylanguages, hardware description languages, and database programminglanguages and technologies) that may be stored, compiled or interpretedto run on one of the above devices, as well as heterogeneouscombinations of processors, processor architectures, or combinations ofdifferent hardware and software. At the same time, processing may bedistributed across devices such as a camera and/or computer and/orserver or other remote processing resource in a number of ways, or allof the functionality may be integrated into a dedicated, standalonedevice. All such permutations and combinations are intended to fallwithin the scope of the present disclosure.

In other embodiments, disclosed herein are computer program productscomprising computer-executable code or computer-usable code that, whenexecuting on one or more computing devices, performs any and/or all ofthe steps described above. The code may be stored in a computer memory,which may be a memory from which the program executes (such as randomaccess memory associated with a processor), or a storage device such asa disk drive, flash memory or any other optical, electromagnetic,magnetic, infrared or other device or combination of devices. In anotheraspect, any of the processes described above may be embodied in anysuitable transmission or propagation medium carrying thecomputer-executable code described above and/or any inputs or outputsfrom same.

While the invention has been disclosed in connection with the preferredembodiments shown and described in detail, various modifications andimprovements thereon will become readily apparent to those skilled inthe art. Accordingly, the spirit and scope of the present invention isnot to be limited by the foregoing examples, but is to be understood inthe broadest sense allowable by law.

1. A method for obtaining three-dimensional data comprising:distributing a medium between a target surface and a sensor, the mediumincluding a single fluorescent substance having a fluorescence emissionspectrum that overlaps in wavelength with a non-zero absorption spectrumof the medium; exciting the single fluorescent substance to provide afluorescent emission; measuring the fluorescent emission with the sensorin a direction of a location on the target surface, including measuringan intensity at a first wavelength and an intensity at a secondwavelength, wherein the medium has a different coefficient ofattenuation for the first wavelength and the second wavelength; anddetermining a thickness of the medium in the direction of the locationbased upon a function of the intensity of the first wavelength and theintensity of the second wavelength.
 2. The method of claim 1 wherein themedium has zero absorption at the second wavelength.
 3. The method ofclaim 1 wherein the single fluorescent substance is fluorescein sodium.4. The method of claim 3 wherein the first wavelength is about 510nanometers and the second wavelength is about 540 nanometers.
 5. Themethod of claim 1 wherein the single fluorescent substance includesquantum dots.
 6. The method of claim 1 wherein the medium includes atleast one of a liquid, a gas, a solid, and a gel.
 7. The method of claim1 wherein the medium is a gas, the method further comprising providing atransparent barrier between the target surface and the sensor to retainthe gas against the target surface.
 8. The method of claim 1 wherein themedium is a liquid, the method further comprising: immersing the targetsurface in the liquid; and positioning the sensor above a top surface ofthe liquid.
 9. The method of claim 1 wherein determining the thicknessincludes calculating a ratio of the intensity of the first wavelength tothe intensity of the second wavelength.
 10. The method of claim 1wherein the sensor measures the intensity of the first wavelength andthe intensity of the second wavelength from a plurality of locations onthe target surface at a corresponding plurality of pixel locationswithin the sensor, thereby providing a two-dimensional array ofthickness measurements.
 11. The method of claim 1 further comprisingconstructing a three-dimensional image of a region of interest with aplurality of measurements from the sensor.
 12. The method of claim 10further comprising constructing a three-dimensional image of the targetsurface from a plurality of three-dimensional images of a plurality ofregions of interest.
 13. The method of claim 1 wherein exciting thesingle fluorescent substance includes directing a broadband light sourcetoward the single fluorescent substance.
 14. The method of claim 1wherein exciting the single fluorescent substance includes directing alight emitting diode toward the single fluorescent substance.
 15. Adevice comprising: a target surface having a region of interest; asensor positioned to measure an intensity at a first wavelength and anintensity at a second wavelength in a direction of a location in theregion of interest; a medium distributed between the target surface andthe sensor, the medium including a single fluorescent substance having afluorescence emission spectrum that overlaps in wavelength with anon-zero absorption spectrum, wherein the medium has a differentcoefficient of attenuation for the first wavelength and the secondwavelength; a light source positioned to excite the single fluorescentsubstance to provide a fluorescent emission; and a processor programmedto calculate a thickness of the medium in the direction of the locationbased upon a function of the intensity of the first wavelength and theintensity of the second wavelength.
 16. The device of claim 15 whereinthe single fluorescent substance is fluorescein sodium.
 17. The deviceof claim 15 wherein the single fluorescent substance includes quantumdots.
 18. A system comprising: a distributing means for distributing amedium between a target surface and a sensor, the medium including asingle fluorescent substance having a fluorescence emission spectrumthat overlaps in wavelength with a non-zero absorption spectrum; anilluminating means for exciting the single fluorescent substance toprovide a fluorescent emission; a sensor means for measuring thefluorescent emission with the sensor in a direction of a location on thetarget surface, including measuring an intensity at a first wavelengthand an intensity at a second wavelength, wherein the medium has adifferent coefficient of attenuation for the first wavelength and thesecond wavelength; and a processing means for calculating a thickness ofthe medium in the direction of the location based upon a function of theintensity of the first wavelength and the intensity of the secondwavelength.
 19. The system of claim 18 wherein the single fluorescentsubstance is fluorescein sodium.
 20. The system of claim 18 wherein thesingle fluorescent substance includes quantum dots.